West, Ian M. 2020. Lulworth Cove, Dorset - Introduction - First and Main Part; Geology of the Wessex Coast of southern England. Internet site: www.southampton.ac.uk/~imw/Lulworth-Cove-Introduction.htm. 19th June 2020. (See also the supplementary webpages on the Purbeck Group west side of Lulworth Cove and Purbeck Group east side of Lulworth Cove.)
Field  guide to the geology of Lulworth Cove, Dorset - First and Main Part
By: Ian West
Romsey, Hampshire,

and Visiting Scientist at:
Faculty of Natural and Environmental Sciences
Website hosted by iSolutions, Southampton University
Aerial photographs by courtesy of The Channel Coastal Observatory
Website archived at the British Library


[2019 revision]





Lulworth Cove - Stair Hole
Lulworth Cove - Fossil Forest - General
Fossil Forest - Purbeck Trees
Lulworth Cove - Dungy Head and St. Oswald's Bay
Lulworth Cove - Durdle Door to Bats Head
Lulworth Cove - Mupe Bay and Bacon Hole
Lulworth Cove Select Bibliography

|Home and List of Webpages |Lulworth Cove Purbeck Group, West Side of Cove |Lulworth Cove Purbeck Group, East Side of Cove |Field Guide Maps and Introduction| |Stair Hole |Fossil Forest |Fossil Forest Purbeck Trees | Dungy Head |Durdle Door |Mupe Bay |Worbarrow Bay |Lulworth Bibliography | | Purbeck Palaeoenvironments | Lulworth Strata and Contained Fossils - more detail| |Durlston Bay - Peveril Point, Upper Purbeck Group |Durlston Bay, Middle Purbeck |Durlston Bay - Lower Purbeck |Durlston Bay - Central Zigzag Part & Coast Erosion |Durlston Head - Lower Purbeck Group and Portland Stone |Durlston Bay - Bibliography
Selected external links: |The Lulworth Estate |Jurassic Coast - World Heritage Site |

Click here for the full LIST OF WEBPAGES

Click or double-click on images for full-size high resolution versions!
(You can download this educational site to SurfOffline, WebCopier or similar software to keep a safe permanent offline copy, but note that at present there is periodic updating of the live version.)

(Note that this is the first and main webpage of three webpages on Lulworth Cove. See above for two continuations on the Purbeck Group on East and West sides)

An introductory overview of Lulworth Cove, Dorset, seen from Hambury Tout, a hill on the west side, 3rd May 2013

A view down to Lulworth Cove, Dorset, from Bindon Hill, above the Chalk cliffs, 18th November 2012

General view of Stair Hole and Lulworth Cove, Dorset, October 2005

A general, broad view of Lulworth Cove, Dorset, 2012

The Chalk cliffs at the back of Lulworth Cove, Dorset, as seen in October 2017, and showing increased erosion in the lower part of the cliff

The changes in dip on either side of the steep fault in the back cliff of Lulworth Cove, Dorset, and some relationship to occasional rock falls

Part of Lulworth Cove, Dorset, seen from the high path approaching the East Horn, 2011

View westward from near the East Horn of Lulworth Cove, Dorset, 16th September 2019

Looking down at a boat from cliff top near the East Horn of Lulworth Cove, Dorset, 16th September 2019

The East Horn of Lulworth Cove, Dorset, showing Purbeck Caps and Broken Beds above Portland Stone, 13th October, 2017

The eastern part of Lulworth Cove, Dorset, seen from near East Point, Petrostrat field trip, 8th September 2012

The site of the former coastguard lookout above West Horn, Lulworth Cove, Dorset, 2011

The west side of Lulworth Cove, Dorset, seen from the beach, 2005

On the Lulworth Cove beach, near the access road and the cafe, looking at the western side of the cove and the West Horn, Dorset, 13th October 2017

Stair Hole, viewed from the western side, with  Lulworth Cove beyond, West Lulworth, Dorset, Wessex coast; students drawing the folds

Southampton University Students receive training in the use of the Right Hand Rule with compass-clinometers, Lulworth Cove, Dorset, October 2011

The eroded and damaged, access point to tbe beach at Lulworth Cove, Dorset, with notes for students or for student exercises, 13th October 2017


Lulworth Cove, on the south coast of England, world-famous for its geology and geomorphology, is the most-visited geological locality in Britain. It is probably the best training location in the world for geology students. There are excellent exposures of folded Jurassic and Cretaceous strata and on the cliffs to the east is the Fossil Forest with an ancient soil and tree remains. There are glauconitic sandstones, sponge chert, cyclical Chalk, oil sands, lignite, ostracods, stromatolites, crocodile and fish teeth, an oyster bed, a transgressive marine pebble bed, a fluvial channel conglomerate, phosphatic strata, carbonate breccias, charophyte limestones etc. etc. The Lower Cretaceous, Purbeck Group is contorted into the Lulworth Crumples at Stair Hole and the spectacular coast around here has caves, natural arches, sea-stacks and high cliffs of nearly-vertical Chalk. It can be studied at all levels from beginner level with basic geomorphology, to inversion tectonics and isotope geochemistry and spectral gamma ray logging. It is compact, very easy to get to, and has all necessary facilities including an interpretation centre. It is used by numerous universities, colleges, schools and societies and there are geological parties there almost every day of the year.

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Related Topics
Lulworth Cove Select Bibliography
Strata at Lulworth - Further Information


1. INTRODUCTION (start):

1.1. Lulworth Cove - Aerial Photographs

Aerial photograph showing Lulworth Cove, the Fossil Forest ledge, Bacon Hole, Stair Hole and Dungy Head, Dorset, Channel Coastal Observatory

Lulworth Cove, Dorset, courtesy of the Channel Coastal Observatory, National Oceanography Centre, Southampton University

Old aerial view of Lulworth Cove, Dorset, modified and recoloured. Copyright

Oblique aerial views of Lulworth Cove, Dorset

Lulworth Cove is a beautiful small embayment providing a fine example of marine erosion in steeply dipping to vertical strata of very unequal resistance. (On the left, it is shown in aerial view with Durdle Door in the distance to the west. On the right we view it, looking south-eastward, from the top of the white chalk path which goes over Hambury Tout and continues westwards to Durdle Door ). The cove is important as an unusual geomorphological feature and also presents excellent exposures of Cretaceous strata with a wide variety of sedimentological, palaeontological and structural features of great interest. The region is one of petroleum exploration, including the sea-floor south of the cove and oil-sands occur nearby. To the east of the cove is the famous Fossil Forest with moulds of fossil trees from the Jurassic-Cretaceous boundary and a fossil soil.

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1. INTRODUCTION continued:

1.2. Topographic Maps

A large topographic map of Lulworth Cove, Dorset, with some safety notes

Large-scale topographic map of Lulworth Cove, Dorset


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1. INTRODUCTION continued:

1.3. Geological Maps

A generalised geological map of the central English Channel from the Isle of Wight to the Cherbourg Peninsula

Geological map of the Lulworth Cove area, Dorset, based on an old edition

The 2000 edition of the 1:50,000 British Geological Survey Map, Swanage, Sheet 343 and part of 342, Solid and Drift - including the Isle of Purbeck and Lulworth Cove

The British Geological Survey map, 1:50,000, Solid and Drift, 2000 Edition, Swanage Sheet, 343 and part of 342, is well worth purchasing from the British Geological Survey website.

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1. INTRODUCTION continued:

1.4. History

Lulworth Cove, Dorset, in 1898 and 1902, after Strahan and Lord Avebury

A visit to Lulworth Cove, Dorset, in 1882 - Robinson

Lulworth Cove, Dorset in the early 1950s (?) with Paddle Steamer Victoria, seen from above

Victorian paddle steamer Empress backs out of Lulworth Cove, Dorset

Webpage author, Ian West at Lulworth Cove, Dorset in 2005, and 1953 with paddle steamer Empress

The cove attracts visitors of all types, more than a million visitors a year at present (House, 1996). It has been much visited by geologists and tourists, particularly since Victorian times, when paddle steamers visits to Lulworth Cove became common.

Further back in time, King George III visited it by boat and was received on the shore with welcoming speeches (Mitchell, 1989). Napoleon, with sinister intention, may, perhaps, have visited (Loader and Loader, 1932), and the poet Keats sailed into the cove on his way to Italy and death (Ashley, 1992).

Smugglers were frequent visitors to the coast here. More recently, two Russian spies landed on the beach in the cove one night during the Cold War, perhaps about 1960. This was the second Russian landing to spy on the Underwater Detection Establishment on the Isle of Portland, Dorset. There is an account of this by Houghton (1972) which is rather amusing.

Footnote - The Portland spy Harry Houghton meets the Russian spies at Lulworth Cove (condensed extracts from Houghton (1972)).
"I passed the message back that I was willing to do my part in a landing at Lulworth Cove,.. I spent a lot of time studying charts and plans We ran through the procedure for getting the two ashore .. The only danger I could forsee would be getting them off the vessel in which they had been taking passage and in to the Cove itself. I asked when the landing would take place. As soon as possible, he said, subject to weather conditions and the Army Artillary practice allowing it. I was to be on call at any time. I was to make a necessity to be in my local at 8.45 pm. Friday.. - I was just about to order my second drink when, to my relief, I was called to the telephone. In our code language I was told that the landings would take place at midnight... needing all my wits about me that evening, I curbed my alcohol intake - and from my swift departure they all concluded I must be ill... I still had time in hand when I got to Lulworth Cove. Having inspected the proposed landing place, I drove up to Durdle Door. I had selected this as the spot from which to give a danger signal if it proved necessary, and wanted to make sure there were no cars or other obstructions. It was quite clear, so I returned with an easy mind to the cove. There I got a bit of a shock. There was now a car close to my parking place, occupied by a couple busy snogging. To be on the safe side I moved off some distance, rather further from the cove than I had anticipated in the first instance. Leaving the car, I went down to the beach, checked that there was no-one else about, and settled down to my vigil. It was a lovely evening so far as wind and sea were concerned: in fact, conditions couldn't have been better. Now that the landings were about to take place I felt strangely unperturbed.. My eyes had got used to the dark by now. I strained my ears to catch the sound of any motor that might be coming in from the seaward, but with the gentle lapping of the waves on the beach I didn't hear it until some seconds after I had already seen it. I guided it in to the landing place with my torch. The boat grounded, the two passengers scrambled out, turned it round nose to sea, and it was smoothly away in the same carefully rehearsed drill as last time. I introduced myself by asking if they had caught any fish, and received the stock reply - "None at all". Whilst shaking hands and welcoming them ashore I was surprised to discover, from the voice and the small, soft hand, that one of them was a woman. We made our way to the car, and I could just discern that she was wearing slacks and had a scarf over her hair, mill-girl style. They had come ashore in Wellingtons, like their predecessors, and when we reached the car changed quickly into shoes which had been fastened round their necks. Both appeared to speak English well. Each accepted a cigarette, and we started on our journey to Ringwood. I had come prepared with plenty of cigarettes, and they chain-smoked almost all the way. Neither carried any luggage. Very little was said to me during the journey.. We hadn't travelled many miles when the man tapped me on the shoulder and said: 'The lady urgently wants to go somewhere.' We were approaching Wareham, so I drove to a public convenience at the Old Granary. There were no incidents on our way to Ringwood. On arrival at the car park I found a car with a white patch on its windscreen as arranged. A man got out of the car and came over to us. It was Gordon [Lonsdale]..." That was the last operation.. Nemesis overtook us a few short weeks afterwards."

Geologists have been visiting since the early part of the 19th Century. Serious studies started here in about the 1830s. Geological publications on the area appear regularly and from time to time reinterpretations are made of the origins of the geological structures and other features.

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1. INTRODUCTION continued:

1.5. The Village of West Lulworth or Lulworth Cove

As a result of the superb geological and geomorphological features and because the locality is of easy access and can take coach parties, Lulworth Cove is visited by large numbers of geologists and geology and geography students. It is one of the most geologically visited places in the UK. It has good facilities for visiting geologists, including a Heritage Centre and shops with books, maps and guides. It is a very popular tourist area and pubs and cafes are situated in the village near to the cove. In the height of summer the area around the cove and Stair Hole has numerous visitors.

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1. INTRODUCTION continued:

1.6. Down to the Cove (from the car park)

The beach where the road comes down to Lulworth Cove, Dorset, from the car park, as seen on 1st October 2011


Arriving at the car park at Lulworth Cove, Dorset


The arrival area of Lulworth Cove, Dorset, at the seaward end of the large car park, probably a suitable meeting place for a geological group


Statue by Jonathon Sells, with carvings showing dinosaurs in peculiar, Victorian style, at the Visitor Centre, Lulworth Cove, Dorset, as seen in October 2017


Walk down to Lulworth Cove, Dorset, on the road past the Doll's House, a former fisherman's cottage, photograph 13th October 2017


The stream which has cut the valley at Lulworth Cove, Dorset, flowing strongly, 27th March 2014


Slope to the beach at Lulworth Cove, Dorset, with boats and with Chalk cliff erosion in the background, 13th October 2017


View of the access to the beach at Lulworth Cove, Dorset, from the Purbeck Broken Beds (breccia) exposure near West Point


Access to the beach at Lulworth Cove, Dorset

The end of the little road down to the beach is between a small cafe and an old boathouse. For field leaders, it is a good place to explain the general aspects of the geology, the basic structure and the mode of formation of the cove.


A minor landslide in the Lower Chalk near the access road down into Lulworth Cove, Dorset, as seen on the 27th March 2014, after the winter storms, and with the beach cafe being demolished


January and February 2014 were times of several severe storms, at least one of them being at about a 1 in 60 year severity. They do not seem to have caused major damage within the sheltered area of the cove, but there has been some erosion of the base of the Chalk Cliffs and a minor landslide in Lower Chalk, as shown above. The beach cafe is being demolished at the time of the photographs. Its base was previously rather undercut, but it is not known at present whether or not the demolition is a consequence of storm damage, or whether there is some other reason. In general, Lulworth Cove does not seem to have suffered the level of damage that took place at the Chesil Beach, Hurst Spit and at Dawlish, Devon.

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1. INTRODUCTION continued:


All cliff have risks! Lulworth Cove is no more dangerous than any other stretch of cliffs in Dorset, in fact much less than some (Lias, Kimmeridge Clay etc), and there have been cliff accidents elsewhere. However, more field parties and people in general go to Lulworth Cove because of its fame. Therefore statistically there is higher chance of an accident in that area in any year. Thus, it is sad that there have been several accidents over several decades, not all involving geologists. The accidents are very few in number in relation to the number of visitors, but great care must be taken, particularly with field parties. Some details of accidents are given to increase awareness and reduce the chances of further accidents.

Rock and debris falls are a serious risk. In particular, the southeastern part of Lulworth Cove where the crumbly Pubeck limestones and shales outcrop should be treated with great caution and the foot of the cliff and overhangs avoided, especially in wet weather. The high vertical cliff at the eastern end of Stair Hole presents a risk of falling blocks, and the foot of this should be avoided. Occasional falls occur at Black Rocks. Obviously cliffs everywhere owe their existence to undercutting and cliff-falls and cannot be totally safe. Geologists and geological parties should avoid wet weather, wear safety helmets where necessary and actively look for impact marks, debris piles, overhangs and other such hazardous places so as to strictly avoid them. Do not loiter in a area of potential rock fall. Under no circumstances shelter under or near rock ledges during wet weather. Rain is liable to dislodge debris from above.

Do not try to climb the cliffs, particularly those of Chalk. Routes which might seem feasible in fact lead to steep crumbly chalk which comes away in the hand. Long ago there has been a fatality on the similar chalk cliffs of nearby Mupe Bay and there have been incidents at the vertical cliffs to the west of Durdle Door. Obviously, some cliff edges of chalk are hazardous and should not be approached. Helicopters have been present on occasions at the chalk cliffs. Stay on the footpath and keep away from cliff edges, and keep children and dogs away.

Adders are occasionally seen in warm weather they usually present little risk unless an attempt is made to handle them. Do not hammer flint or chert as these produce high velocity splinter which can damage eyes.

There can be risk from the sea in the area in storm conditions. Appropriate warm and waterproof clothing may be needed and leaders should be prepared to cancell trips if necessary.

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1. INTRODUCTION continued:


Accident Risk - South of East Over

Part of the cliff section to the south of the East Over promontory, where there is an overhang, has a particular risk. There was a fatal accident in 1977 at the Hard Cockle overhang here, when a party seems to have sheltered from steady rain. Three students and a teacher were killed.

For details of the accident go to:
Lulworth Cove continued, Purbeck Group, East Side of Cove )

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1. INTRODUCTION continued:

1.9. SAFETY - continued

Accident Risk - Black Rocks

The Black Rocks are a set of old fallen blokcs situated at the back of Lulworth Cove just east of the road down to the beach and the cafe. The Black Rocks consist of Upper Chalk with flint and have fallen from the overturned strata above the major east-west fault in the cliff. Falls from the source beds high in the cliff are very rare. There was an accident in 1957 when a significant rock fall took place, but fortunately no-one was killed. For more details go to: Lulworth Cove Introduction - The Black Rocks, Rock Fall Locality .

Another accident took place here in 2009 and again, fortunately no-one was killed. It is not clear as to whether this was connected with the Black Rock type of fall. It may have been the result of movement of low-level Chalk debris. Here is an extract from a press report (Steven Smith, 2009).

"Nine-year-old boy who was buried by rocks at Lulworth Cove is discharged.
8:10am Tuesday 22nd September 2009 in News By Steven Smith
Danger: Lulworth Cove was the scene of a horrific accident on Sunday, when a cliff fall (location marked by asterisk [Black Rocks area] buried alive a boy of nine.
The nine-year-old boy thought to have been seriously injured when he was buried under rocks was discharged from hospital yesterday, Coastguards said. He was completely covered by the falling rubble on Sunday as he played in the late summer sun at Lulworth Cove. Initially it was thought that the child had serious spinal injuries, but yesterday he was discharged from hospital, a Coastguard spokesman confirmed. He said: "It,s all round good news, if you consider the situation. It's an unpredictable event of being in the wrong place at the wrong time; it had a very successful outcome."

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1. INTRODUCTION continued:

1.10. Conservation

Education parties here will have plenty to see and plenty to do without really needing to use hammers. Conservation needs particular emphasis here because of large numbers visiting. Instead of hammers have hand lenses, compass clinometers, hydrochloric acid, notebooks, maps and planned project work . Occasionally something of importance may need to be collected for laboratory investigation or a rare fossil may be destroyed by erosion if left in the cliffs. It is undesirable for large parties to use hammers and there is little to hammer here because the cliffs are sea-eroded and good collectable fossils are not abundant. Hammers may not be used within the Army Ranges, as for example at the Fossil Forest or Mupe Bay.


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. 2. STRATIGRAPHY (start):

2.1. Stratal Succession - General

Simplified diagram of the stratal succession in the Lulworth Cove area of Dorset, England

This diagram the simplified succession of strata in the Lulworth Cove region. The thicknesses given are only approximate and most units thicken in an eastward direction. FF - Fossil Forest horizon, LGS - Lower Greensand (very thin or absent here), PL - plenus marl, a grey marl marking the boundary between Lower and Middle Chalk. More detail is given in sections on specific formations.

2. STRATIGRAPHY continued:

2.2. General

Cliffs from White Nothe to Worbarrow Bay, Dorset. Old diagram

This diagram shows the strata in the cliffs of the region as seen from the sea. The Chalk zonal scheme shown is that of Rowe and Sherborn (1901) .

Simplified geological map of the Lulworth Cove area, Dorset, Wessex Coast

Simplified geological map of the coast from Lulworth Cove to Worbarrow Bay, Dorset, Wessex Coast

Old geological map of Lulworth Cove and Worbarrow Bay, Dorset

The upper map is a simplified geological map of the Lulworth Cove area is based on Townson ( 1975b) with some modifications based on the old edition of the British Geological Survey map of Swanage (sheet 343 and part of 342). The middle map provides the simplified geology further east so as to include Worbarrow Bay. For details consult the British Geological Survey map - Swanage, Sheet 342 and part of Sheet 343. This differs in detail from the old edition of the British Geological Survey, Weymouth Sheet 342 which covers the Lulworth - Worbarrow coast. The simple maps shown here are intended for initial introduction. Part of an old geological map (bottom) is also provided for comparison.

The dip in the Portland, Purbeck and Wealden strata is steep and to the north. The synclinal axis can be recognised by the long narrow Tertiary outcrop north of the cove. This axis runs east-west. The main axis of the very asymmetrical anticline is under the sea, at the Lulworth Banks, south of the map. The steeply dipping strata is part of the north limb which runs along the coast. The locations of some of the many notable geological features here are shown. Localities east of those described in this particular guide (the Fossil Forest and Mupe Bay etc.) are in the military firing ranges, which are open most but not all weekends. Those discussed below, including Lulworth Cove, Stair Hole, Dungy Head and Durdle Door, are accessible at all times. A more detailed geological map is provided below.

Exposures of the strata indicated in the map above can be seen in aerial photographs. The cove has been described in the past as "an almost circular bay or basin, about five hundred yards [metres] in diameter; formed by the action of the sea on the receding Chalk [but in fact the Chalk has not receded much; more Wealden has been lost]. The rocks at the entrance on both sides of the cove being composed of the Portland and Purbeck strata, have been less affected. These last are highly inclined and contorted, while the Chalk and Wealden Beds are nearly vertical." (Damon, 1884).

The entrance is a breach in the very resistant Portland Stone about 120 metres wide. The overlying Purbeck Group has been cut back at an angle until sheltered by the Portland Stone. The incoherent sands and clays of the Wealden have been more extensively eroded to produce the circular shape of the cove. The Chalk at the back (north side) is only being eroded slowly.

The strike of the strata is east-west. In the aerial photographs above you can see the submerged extensions of the Purbeck limestones from the Points at the south side of the cove, the westward extension of Wealden sandstones from the east side (Coarse Quartz Grit etc) and also an east-west Chalk/UGS outcrop near the north shore. None of this suprising. There does not seem to be a fault between the two Points, which some people have suspected was present. Perhaps divers can discover just what are the two strange oblique submerged ridges in the central to eastern part of the cove They do not fit the expected pattern. Are they faults or what?

Footnote: Channel Coastal Observatory
Excellent, high resolution aerial photographs are available for Lulworth Cove and other parts of the Wessex coast. To see ECW files an ER reader is available free on the internet and this should be obtained first. Then go to Channel Coastal Observatory , which like this website, is based at the National Oceanographic Centre, Southampton. Follow the instructions and register and obtain a password which will be confirmed by email. Then log on and go to the section on Map Viewer and Digital Catalogue. Find by zooming on the coast or other methods the appropriate ECW files, and download to your computer. This is a free public service and the photographs obtained are superb.

Topographic  Map of Lulworth Cove

As shown on the topographic map, the village, slipway and jetty are at the low northwestern part of the cove. The stream and valley might follows the northern course of a fault, although this is not shown on a detailed geological map below of Nowell (1997). The cove is a feature that has developed at a site of river-breach (Poole, 1987). The stream which now flows into the cove would at least at this point have followed the line of a known fault under the water of the cove and cut a valley into the outer ridge of Portland and Purbeck strata. There is no other direction in which it could have flowed and the size of its valley is too great for it to have been a very recent feature. Simplified diagram of the stratal succession in the Lulworth Cove area of Dorset, England

Major lithostratigraphic units of the Lower Cretaceous of Dorset, England in approximate relationship to the chronostratigraphic stages

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2. STRATIGRAPHY continued:

2.3. Geological Maps - More Details

The 2000 edition of the 1:50,000 British Geological Survey Map, Swanage, Sheet 343 and part of 342, Solid and Drift - including the Isle of Purbeck and Lulworth Cove

Detailed geological map of Lulworth Cove

This detailed geological map of the area around Lulworth Cove is based on Nowell (1997). This is a good map for showing proven and hypothetical faults not indicated on other, simpler, maps. Notable is fault N trending northwest-southeast through the mouth of Lulworth Cove. Such a fault is clearly the structural feature responsible for locating an original stream valley through the Portland Stone here. Sea erosion subsequently broke through at this weak point. It might be argued that this fault extends northwest up the present stream valley of Lulworth Cove; Nowell, however, shows the fault as terminating against major east-west faults. This is an interesting point for discussion on a field trip and evidence could be sought for and against this argument in the northwestern part of the cove.

Related to this is record on the map of the north-south Hambury Farm Fault (marked with an L), north of Stair Hole. It is very clear when walking up the path from Lulworth Cove onto Hambury Tout in the direction of Durdle Door that the Chalk downs do not line up in an east-west direction. Hambury Tout is displaced northward in relation to Bindon Hill. Nowell does not relate this displacement to a strike-slip fault on the line of the stream but to this north-south dextral fault with a lateral displacement of about 100m. Look at fault N on the map. Could you extend it to get the same effect? Can you see a problem with such an attempted explanation? Yes, it is shown as sinistral, not dextral, in the Purbecks within the cove. But now look carefully at fault I, on the western part of the map, from Hambury Tout to Dungy Beach. Make a comparison.

A controversial aspect of the paper by Nowell is the correlation of quartz grits within the Wealden Group and whether the Coarse Quartz Grit is one bed throughout eastern Dorset as most authors have considered. Nowell correlates the prominent quartz grit (the "Coarse Quartz Grit") of Lulworth Cove with the lower of two quartz grits at Mupe Bay. Radley (1998) takes issue with this new scheme. See the paper of Nowell and the discussion of Radley and reply by Nowell to find out more about this argument. See also the Mupe Bay Field Guide for more information.

( The meaning of most of the symbols on this map is clear and I have added some text; D refers to the "Durlston Formation", the Purbeck Group from the Cinder Bed upwards, and L the "Lulworth Formation", the strata below the Cinder Bed. S refers to the Portland Sands. The original paper should be consulted for more information. It refers to an unpublished map of the area around Lulworth Cove by Dr C.R. Bristow and acknowledges Dr E.C. Freshney for finding faults at Dungy Head and the back of Lulworth Cove. Fig. 6 in this paper provides another version of Bevan's (1985) cross section ,located just west of the cove. For discussion of some aspects of geomorphology of Hambury Bottom and the Lulworth Cove valley see also Burton, 1937).

Go to More Information on the Succession of Strata and Contained Fossils?

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The Portland Stone is exposed on the outer sea cliffs. In general it cannot be reached without climbing, although the top can be seen by an easy scramble at the Fossil Forest exposure. For more information go to:


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4. STRATIGRAPHY - Purbeck Group

For more information go to:


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5.1. East Side of the Cove

See also: Wealden at the west side of Lulworth Cove.

Simplified diagram of the stratal succession in the Lulworth Cove area of Dorset, England

Major lithostratigraphic units of the Lower Cretaceous of Dorset, England in approximate relationship to the chronostratigraphic stages

The Wealden fluvial and mudflat strata are only 166m in thickness just here (Arkell, 1947). They are abnormally thin because the Wealden Group reaches about 750m in thickness at Swanage, further east. It is necessary, of course, to consider whether the various parts of the thick sequence are uniformly thinned (the Purbeck Group tends to do this but not perfectly so) or whether a large part of the sequence is missing. On the east side of the cove the Wealden is steep dipping and almost vertical in parts, but rarely overturned as they are on the west side.

The main characteristics of Wealden strata in the Wessex region can be summarised as:

1. Clays and silts with sandstones, of the Lower Cretaceous System; deposited from about 146-125 million years ago.
2. No limestones are present, and there are no typical shales of marine type (i.e. like Kimmeridgian) in Dorset.
3. Marine fossils are generally absent, but freshwater and brackish water fossil occur.
4. Clays often show palaeosol weathering and oxidation - reddish or purple colours.
5. Some sandstones are coarse and show channel features and cross-bedding.
6. Lignite (black, carbonised fossil wood) is common throughout.
7. The Wealden is the source of most of the British dinosaur bones, particularly in the Isle of Wight; the name 'dinosaur' was first applied to the remains of an animal found in the Wealden.
8. Very shallow water facies are dominant, with dinosaur footprints on the Isle of Wight and elsewhere.
9. Oil sands occur.

There is an extensive literature on the Wealden of southern England. The Wealden of the Weald (southeastern England) has been much studied by the late Professor P. Allen. He originally put forward a deltaic model but later realised that everything was of very shallow water origin. What he had once regarded as pro-delta clays proved to contain dinosaur footprints. In his later interpretation - Allen (1976) "Wealden of the Weald: a new model" he explained the evidence for palaeoenvironments of coastal mudplains with lagoons and sandy water-courses. This paper makes interesting reading, summarises earlier evidence and provides references to most of the earlier publications. The work on the Wealden of the Weald does not explain in any detail the western areas like Lulworth Cove. Understanding the southeastern mudplains and rivers helps interpret the Wealden of the west. The general view is that to the west, as here in Dorset, the Wealden is more fluvial in character.

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5.2 WEALDEN GROUP continued

East Side:
The Coarse Quartz Grit

Two views of the Coarse Quartz Grit, Wealden Group, Lulworth Cove, Dorset

The Coarse Quartz Grit in the Wealden on the east side of Lulworth Cove, Dorset, with details labelled; photo June 2000

Details of the Wealden Coarse Quartz Grit at the east side of Lulworth Cove, Dorset, in 2004.

The top of the ridge of the Coarse Quartz Grit on the east side of Lulworth Cove, Dorset, with the Moon above

Quartz and chert pebbles in the

(for comparison here is the Coarse Quartz Grit at Worbarrow Bay, where the exposure of the Wealden is much better and the dip is less. See the Worbarrow Bay website - Wealden section.)

The Coarse Quartz Grit in the cliffs of Worbarrow Bay, Dorset, Dec 2003

Coarse Quartz Grit, examined by students, Worbarrow Bay, Dorset

There is a prominent exposure of the Coarse Quartz Grit at the east side of Lulworth Cove. As you can see it is not as well exposed as at Worbarrow Bay, but the cliff is still informative. The bed show a channel features produced by the Wealden river. It is multistorey, that is there are fine pebble beds one on top of another. At times the channel was abandonned and logs were washed into into it. These are preserved as lignite, somewhat squashed by the weight of overburden. Bones of dinosaurs are sometimes found in channel deposits like this. I have found an Iguanodon tooth in the equivalent bed at Swanage.

It is easy to see that many of the small pebbles here consist of vein quartz. The nature of the black ones cannot satisfactorily be determined in the field. Some are of black chert, usually known as "lydite", others are of tourmalinised quartzite. All are hard and resistant. Gardner (1957) has provided more details and discussion. He gave the composition of the Coarse Quartz Grit at Lulworth Cove (for the -3.5 phi particle size) as - opaque quartz - 28, radiolarian chert - 25, quartz plus tourmaline - 24, translucent quartz - 13, fibrous quartz - 10. Allen has found a clast at Durdle Door in the same bed to be of Precambrian age (Allen, 1972). This has brought up interesting problems about a source of old tourmalinised detritus in the west. Armorica (Brittany) is a large area of very old rocks and could have provided debris for the Wealden river (there is, after all, Wealden in the English Channel north of Brittany). Allen points out, though, that there is a problem of finding tourmalinisation of Precambrian date there. He also discussed the possibility of some derivation from a former extension of a Newfoundland Grand Banks area, since fragmented by sea-floor spreading. There is little doubt that the Wealden river came from the west but its details are still uncertain.

Much of the remainder of the Wealden consists of finer, overbank rather than channel, sediments. There are clays and silts from the floodplains, oxidised in a patchy manner and forming gley soils. These are now the variegated marls. Some sandstones might be crevasse splay sands (sand deposited on the flood plain when floods splay out from breached levees or banks of a channel). A better place to study the sandstones, though, is Worbarrow Bay. Ironstones are usually siderite, although some pyrite occurs. The iron comes from chemical weathering beneath the forest soils and then transport into the rivers. In fluvial environments it is often concentrated as the iron carbonate siderite, rather than pyrite, the iron sulphide, because of relative deficiency of sulphate ions that are available in abundance in seawater (sulphate-reducing bacteria convert the sulphate to sulphide and then iron is trapped by the sulphide ions as pyrite).

Brick Kilns on Wealden at east side of  Lulworth Cove

The succession (Arkell, 1947) is as follows (from top down to bottom):

(probable thin Lower Greensand above)
Variegated marls and sands - 26 m.
Four or five bands of soft ironstone - 1.5 m.
Variegated marls and ferruginous sands - 30 m.
Coarse Quartz Grit (which we have just seen)
Variegated marls and sandstones (lower beds are partly obscured; they were formerly worked for bricks and you can see remains of the brick kilns in the photograph, shown here). Arkell (1947) comments on black oil sand here. I think that the black bed visible now is carbonaceous (with plant debris) and if you would like to see a good oil sand in the Wealden go to Mupe Bay. Thickness of the variegated marls and sandstones - 70 m.
Variegated marls and sandstones, exposed intermittently - 34 m.
(Purbeck Group below)

Total Wealden Thickness - 166m. (544 feet). Strahan, 1898, recorded the beds above the Coarse Quartz Grit as 40 feet (12m.) thicker, perhaps because of measuring at the foot of the cliff, unlike Arkell who measured in the upper part. Thus it is possible that the Wealden reaches 178 m. here, but this is not certain )

Examine the finer Wealden sediments and lignite, with a thought for (very rare) dinosaur remains. Then continue down stratigraphically to the Purbeck Group at East Over (where the limestones project forward). There is a path up the cliff here, if you want to go to Pepler's Point with a high viewpoint over the cove and, perhaps, on to the Fossil Forest. Otherwise continue to the Purbeck Group at the foot of the cliffs as shown below.

Lulworth Cove, Dorset

The photograph above shows a possible effect of the Lulworth Crumples on the Wealden strata. It is very obvious at Lulworth Cove and Stair Hole that the the Purbeck Group is folded with minor folds within the major structure. The Wealden is also distorted and a careful examination of Stair Hole will reveal overturning in relation to the Crumples in the main Purbeck cliff section. Here, on the east side of Lulworth Cove we seem to observe minor effects of the Crumple folding. There is an altenative explanation, though. These structure could be the result of minor thrust faults northward (of S3a type). The lower one does seem to show a fault plane. Of course, they could be both fault structures and consequences of Crumple development to the south. Look for evidence in relation to origin.

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5. WEALDEN GROUP continued

5.3. West Side of Lulworth Cove

With regard to Wealden strata, see also for comparison:

Coram, R.A., Radley, J.D and Martill, D.M. 2017. A Cretaceous Calamity, the Hypsilophodon Bed of the Isle of Wight, Southern England. (by Robert A. Coram, Jonathon D. Radley and Professor David M. Martill). Geology Today, Vol. 33, No. 2, first published 15th March 2017, pp. 66-70. In Wiley Online Library.
[This paper is very relevant to the extensve Wealden exposures at Worbarrow Bay and the smaller exposures at the eastern side of Lulworth Cove, although Hyosilophodon remains have not been recorded there. It is particularly of sedimentological interest since some of the Lulworth Cove and Worbarrow Bay, Wealden strata may have been deposited in conditions similar to those postulated..][more data is in lulref.htm webpage - webpage on Lulworth Cove geological literature]


Slumped Wealden cliffs on the west side of Lulworth Cove, Dorset

The Wealden is exposed in a patchy and irregular manner in low, slumped cliffs on the west side of the cove.

Nowell (1998) noted that the units within the Wealden succession are thinner here than on the east side of the cove. He considered that this supports the view that the mouth of the cove was cut by a fault that was active during deposition of the Wealden strata. The evidence of growth faulting in the area is also known in the Purbecks ( West, 1975) but mainly in relation to a fault in Worbarrow Bay.

The top of the Wealden sequence on the west side of the cove is cut out by an east-west fault, according to Nowell (1998).

Some details of the Wealden here will be considered.

Simplified diagram of the stratal succession in the Lulworth Cove area of Dorset, England

Thin sandstones in the Wessex Formation of the Wealden, west side of Lulworth Cove, Dorset, 2005

Here are some interesting, thin and lenticular sandstone bodies in the Wessex Formation. They seem to be of fine or medium-grained sand, quite unlike the Coarse Quartz Grit. Note that the direction of younging in these slightly overturned strata is towards the north (to the right of the photograph). If you look carefully at the small channel-like feature in one of these you will some ichnofossils or trace fossils.

Worm burrows at the base of a sandstone,  Wealden, West side of Lulworth Cove, Dorset, 2005

The worm burrows shown here seem to be of Planolites. This occurs in the Vectis Formation, which represent the upper and brackish to marine part of the Wealden Group in the Isle of Wight ( Stewart, et al., 1991). It is not usually present in the fluvial facies of the Wessex Formation that is present here at Lulworth Cove. Probably this occurrence needs further investigation.


Lignite in the Wessex Formation of the Wealden Group, west side of Lulworth Cove, Dorset, 2005

There is a small sequence of weakly cemented sandstone with lignite. This is partly overturned. The origin of it is of interest. A general photograph is reproduced here again for location purposes.

Slumped Wealden cliffs on the west side of Lulworth Cove, Dorset

Wealden sands with lignite, Lulworth Cove, Dorset, Nov. 2005

Wealden sands with lignite, Lulworth Cove, Dorset, Dec. 2005, details with cross-bedding

Compaction features in lignite within sandstone, on the east side of Lulworth Cove, Dorset, 16th September 2019

The sandstone with lignite is interesting. The sandstone is fine to medium grained; it does not show obvious coarsening-up or fining-up. It is appreciably cross-bedded and the lignite drapes on foresets and in small channels. Was it the deposit of a rather low-energy river channel. Has there been lateral accretion from the growth of small point bars? The compaction has been very great. The lignite has been fractured in a rectilinear manner, that is as small rectangles of black lignite. Under the great compaction forces, the rectangular pieces of lignite have oftenb been separated by some intervening sand.


A sudden, high-energy flood of freshwater surged eastward during deposition of the Lower Cretaceous Wealden strata, this is presumably the result of a sudden, very severe rain storm, about 140 million years ago


[see also

Coram, R.A., Radley, J.D and Martill, D.M. 2017. A Cretaceous Calamity, the Hypsilophodon Bed of the Isle of Wight, Southern England. (by Robert A. Coram, Jonathon D. Radley and Professor David M. Martill). Geology Today, Vol. 33, No. 2, first published 15th March 2017, pp. 66-70. In Wiley Online Library.

[relevent extract:]
"The upper part of the Lower Cretaceous Wealden Supergroup (Barremian-early Aptian; approximately 130 to 122 million years old) on the Isle of Wight comprises the Wessex and Vectis formations, both of which are well exposed in the cliffs of Brighstone Bay on the south-west coast of the island (Fig. 1). The older Wessex Formation, comprising multi-coloured mudstones and sandstones, was deposited in and around meandering river channels. The climate was warm to very hot and of Mediterranean aspect; hot, dry spells punctuated by heavy rainfall that transformed the ancient Wessex river floodplains seasonally into swampy wetlands."

[relevent extract:]
"Most of the dinosaur remains are found in what are commonly referred to as 'plant debris beds': grey-green silty mudstones that contrast markedly with the predominantly red and variegated mudstones and sandstones making up most of the formation. The PDBs (as they have become known) may reach 1.5 metres thick, although they are usually considerably thinner (1-30 cm) and are generally of limited lateral extent (tens of metres). Most conspicuously, they are packed with pieces of black lignitized wood, commonly pyritized and sometimes burnt, and pebbles of calcrete. This, along with the less frequent bone material, is interpreted as terrestrial debris transported to ephemeral ponds, abandoned channels and other depressions on the river floodplains by storm-induced floods. The dinosaur remains are almost always incomplete, often merely isolated bones, the dead bodies clearly having remained unburied for long periods and the bones often scavenged, scattered, trampled and sometimes water-worn. The diversity of dinosaur remains in plant debris beds is high, and includes ornithopods, thyreophorans, sauropods and theropods."

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6.2 STRATIGRAPHY - Lower Greensand

(Notes to be added)

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7.1. Introduction:

Simplified diagram of the stratal succession in the Lulworth Cove area of Dorset, England

General view of the eastern exposure of the Albian, Gault and Upper Greensand, Lulworth Cove, Dorset, England

Basal Gault Pebble Bed at the eastern Albian exposure at Lulworth Cove, Dorset, England

The name "Gault Clay" is a tautology - "Gault" is an old English word for clay, as in "Gaulters Gap", Kimmeridge where there is no geological Gault. In southeastern England the Gault is a purer black clay, but here at Lulworth Cove is very sandy and largely a black or dark grey loam. It passes up transitionally into the Upper Greensand, gradually becoming more sandy and greener and more glauconitic. The Gault, known in the Isle of Wight as the "Blue Slipper" is a common cause of landslides. The result of this is that it is not well-exposed on the Dorset coast, and is often concealed by debris. Further east in the Weald area, the Gault Clay is a black clay about 30 to 80 m in thickness. The boundary between the Gault and the Upper Greensand is diachronous [from the Greek - "across time" - diachronous refers to the crossing of time planes], and is usually quoted as the best example of diachronism in Britain.

The Gault is well-known for its good aragonitic fossils, such as ammonites of the genus Hoplites and its relatives (usually small compressed subinvolute shells with strong ribs). These are not normally found at Lulworth because the exposure is poor. Only some bivalves have been found, and these in boulders in the talus.

If the Gault is regarded as the black, more argillaceous beds of the Albian sequence, then the thickness at Lulworth Cove of these is only 11.3 m according to Arkell (1947). Contrast this with the 34 m of black beds, clay and loam of the "Gault" at Worbarrow. No less than 23 m have been lost in that short distance. This type of change is like that seen in the Jurassic strata affected by Late Kimmerian extension regime. So, although the Albian was deposited round about the end of this phase, the switch to the compressional phase may not have been completed at that time. In other words Lulworth Cove was still, even at this late stage, showing more "high" characteristics than Worbarrow, which is transitional to "basinal" in term of facies and thicknesses (there is even some Albian - Purbeck analogies in local variations West (1975) ).

Gault-Wealden Junction at Dungy Head

This diagram explains some characteristics of the Dorset Gault. Notice that the clay mineral composition contains the expandible clay mineral smectite, whereas this is generally absent in the continental Wealden. The properties of the "Blue Slipper" are affected by the presence of the expandible and greasy smectite. In the Wealden, in contrast the acid soil conditions of the early Cretaceous would have been adverse to the preservation of smectite and more favourable for kaolinite.

Notice that the Wealden palynomorphs shown are Hauterivian. Is there any Barremian here? Of course, there is a hiatus anyway; there is no Aptian so the Barremian could be missing too. The dinocysts are interesting; these are late Albian. This ties in with the reduction in thickness of the Gault in the Lulworth Area; presumably the lower beds are missing. The exact age of the pebble bed is probably uncertain. Perhaps this is diachronous and also rather young.

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7. GAULT CLAY continued -

7.2. Gault Overstep

Overstep of the Albian Gault and Upper Greensand in southern England, schematic

The base of the Gault is probably the most well-known horizon in Britain for overstep. This is the "stepping over" of a stratum above the angular unconformity from younger strata to older in a particular direction. If the angle is great the overstep may be actually visible in the field but this is rarely the case. More often the angle of the unconformity is very small and the overstep is recognised from stratal relationships over a significant distance.

As shown above, the Gault commences with a pebble bed that marks the major unconformity at the base of the Albian. On a broad scale there is pronounced overstep westward, as shown in the diagram above. This new and drastic phase of the tilting of England and Wales towards the east commenced at this time. It still continues: London and the East Coast is still going down (note Thames Barrier).

Hypothetical section through Lulworth Cove, Dorset, modified after one by House, based in turn on the work of previous authors

Now, to consider further the problem of overstep of Albian examine again a N-S cross sections through Lulworth Cove. The Gault oversteps quite abruptly onto the Corallian and other Jurassic strata. At White Nothe, east of Weymouth, you can observe the Gault and Upper Greensand on the Kimmeridge Clay. This northern overstep is shown on the diagram as mainly due to inversion [reversal of direction of throw over time] on the fault. You can see though that pre-Albian folding is also involved, and this is visible at White Nothe. Observe also that directly north of the Inversion boundary fault the direction of overstep is locally opposite and is actually from north to south.

Thus, the east-west diagram is a simplification, but important in showing the broad features. Go west to Lyme Regis or Charmouth, look at Black Ven, the Gault and Upper Greensand are on Lower Lias clays - and the westward overstep becomes very clear. Local overstep in the Lulworth area is complicated because here we are at the northern margin of the English Channel Inversion.

In broad structural term, the Basal Gault Pebble Bed marks a drastic change in tectonic regime here. In the Jurassic to the early Cretaceous the Wessex region was off the east coast of America, there was N-S extension of the developing English Channel Basin. Later the Wessex region was separated from America by the North Atlantic Ocean. Then came the gradually developing N-S compression from the African Plate, and in due course, the Alpine folding. The Basal Gault Pebble was formed at the very end of the extension phase and is associated with the Late Kimmerian movements and unconformity.

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7. GAULT CLAY continued:

7.3. The Basal Pebble Bed

Basal Gault Pebble Bed at the eastern Albian exposure at Lulworth Cove, Dorset, England

Basal Gault Pebble Bed at St. Oswald's Bay, west of Lulworth Cove, Dorset

The Basal Gault Pebble Bed on the NE side of Lulworth Cove is shown again above, together with a photograph of the same pebble at St. Oswald's Bay, where it is sometimes better exposed. This is a good example of the classic relationship of a basal pebble bed to an unconformity. Because the strata are steeply folded the stratum is almost vertical and is overturned in some places. Younging is to the north.

Description of the stratum

Very useful information on the Basal Gault Pebble Bed has been provided by Garden (1988) who studied the sections at Durdle Door promontory (SY 806803) and St. Oswald's Bay east (SY 816800). The pebble beds are O.5-0.7m thick, and contain cobbles and pebbles set in a muddy, ferruginous sandstone and fine rapidly upward into micaceous mudstones. Garden (1988) found that where the exposure is good intensive bioturbation can be seen in the basal sandstones. Burrows also extend down into the underlying Wessex Formation (Wealden) siltstones and sandstones to depths of O.l5m. You may or may not see this at Lulworth Cove.

The pebble suites

The bed is an example of a fairly mature pebble bed and the components are mostly composed of silica, notable for its resistance. The phosphorite, mentioned below, has a hardness of only 4.5 to 5 on Moh's Scale and although, less resistant, it has probably not been transported very far. Garden (1988) reported (p. 45 and p. 211) that the the pebble suites of the basal Gault Pebble Bed of east Dorset (i.e. Lulworth area) are trimodal. The three main groups are as follows:

1. Large pebbles - coarse-pebble to cobble-grade clasts of pale, weathered cherts and dark phosphorites. He found at Durdle Door and St. Oswald's Bay cobbles of up to 450 mm, almost half a metre, of pale-coloured weathered chert. The weathered chert is very interesting with regard to Lulworth Cove and region. Garden (1988) pointed out that they are typical Portland Group cherts, including the Rhaxella cherts (the dominant sponge cherts of the Portland Cherty Series), oolitic and coarse-grained bioclastic chert. There is some Purbeck chert of silicified evaporite type from the basal Purbecks and also silicified freshwater limestone of Cherty Freshwater Member type.
2. Small pebbles - small rounded pebbles of vein quartz, tourmalinite (mostly microcrystalline quartz and tourmaline - tourmalinised mudstones or cherts, but tourmalinised breccias and coarse quartz with acicular tourmaline is also present) and sandstone (quartzites).
3. Small phoshorite pebbles - a minor group - subangular to subrounded clasts of brownish black phosphorite up to 35 mm in length. Phosphorite clasts in the Basal Gault Pebble Bed include bivalve (Protocardia) and ammonite casts from the Kimmeridge Clay.

A notable aspect of Garden's (1988) research is that Carboniferous chert is rare in the Basal Gault Pebble Bed in the Lulworth region but that Jurassic Portland chert is abundant, particularly at Durdle Door. This, of course, all accords with the overstep northward of the Basal Gault Pebble Bed onto the Portland Group, a feature which is seen in the field at White Nothe. For further details see Ross Garden's (1988) thesis.

Origin of the pebble bed

This pebble bed represents shoreline retreat Garden (1988); it is a relic of a shingle beach of the mid Albian marine transgression migrating across this tilted land (Owen 1971). Because of the local overstep northward onto Lower Cretaceous Jurassic strata, the pebble bed includes clasts of material from the Wealden Coarse Quartz Grit, particularly vein quartz pebbles. The chert derived from the Portland Group has come from a cliffed coastline, not very different from that of the Isle of Portland at the present time. Back in geological time the Albian coast was very similar in many respects to the present Dorset coast. At most other times there were no significant cliffs and a quite different geomorphology. Both the Albian pebble bed and the modern pebble deposits of Dorset like the Chesil Beach are transgressive deposits above a plane of unconformity (both with westward overstep).

Garden (1988) considered that the poor sorting of the bed and the presence of clay-filled burrows extending down below the unconformity indicate that the deposits are unlikely to be high-energy, upper shore face deposits. The mixing of gravel, sand and mud is more consistent with deposition in the nearshore zone on the lower shoreface


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8.1. UGS Introduction

Simplified diagram of the stratal succession in the Lulworth Cove area of Dorset, England

Albian (Upper Greensand) and Chalk divisions, zones and stages in Dorset, England

Upper Greensand  and basal Cenomanian - stratigraphy and zones for the Wessex area, England

Lateral facies changes in the Upper Greensand and basal Lower Chalk on the Dorset coast, England

Access to the beach at Lulworth Cove, Dorset - with Upper Greensand

Location of Upper Greensand at Lulworth Cove, Dorset

Upper Greensand at Lulworth Cove, Dorset

To start on a tour of the geology of Lulworth Cove, one can first look at the general features from the shore near the beach cafe. Then a short distance eastward along the beach, and just after the huts the Upper Greensand is seen, as in the photograph above. This unit is mostly of Albian age (Cretaceous) and is about 40 metres thick in this area. For details of stratigraphic classification see the diagrams above and refer to the paper of Drummond (1970) which contains much of interest to anyone studying the Lulworth area.

The Upper Greensand is a greenish, glauconitic, calcite-cemented sandstone, argillaceous in the lower part, and entirely of marine origin. Notice in the photograph above how the softer, lower part (in the left and centre of the picture) gives way stratigraphically upwards (to the right) into harder more carbonate-rich sandstone. There is much bioturbation and burrows are obvious.

The green mineral glauconite occurs as rounded grains, appearing almost black under a hand lens, and this is a soft silicate mineral, a type of clay, but green and in granular form. The glauconite grains are sand-sized, ovoid or spherical aggregates of dark green, iron-bearing clay minerals. There are separate smectite, illite and mixed-layer varieties so the broad term "glaucony" is sometimes used to refer to a green glauconite-type mineral of unspecified clay mineral composition. The mineral contains both ferrous and ferric iron and the implication of this is that it has been formed at the oxic/anoxic boundary (i.e. with normal oxygenated water above reduced sediments). The rounding of the grains is a result of current or wave activity, also shown by the presence of quartz sand. Sea-floor conditions were probably rather like those of the current swept English Channel at the present day, but appreciably warmer.

It is not certain as to why glauconite was so abundant in southern England at this time, but the shallow current-swept sea-floor and the relatively ambient temperatures weres probably important factor. The same facies reappears in the Middle Eocene Bracklesham Group of Hampshire and Isle of Wight, where there are greensands with similar scallop shells Amusium corneum. At this time, too, the temperature was relatively high for the palaeolatitude. It also occurs in the Portland Sand, and there is an anomalous freshwater variety present in the Upper Purbeck strata of Lulworth Cove, and elsewhere.

Chert that has formed from sponge spicules in the Upper Greensand,Lulworth Cove, Dorset, 2005

In the upper part of the Upper Greensand (that is further east) there is much chert; the silica for this has come from opaline sponge spicules. These are sometimes visible if the rock is examined carefully with a good hand lens, although they are now probably chalcedony.

The top of the Upper Greensand is remarkable here in containing a thick boulder bed. The boulders are of calcite-cemented, glauconitic sandstone that have been rolled around by storm waves on the sea-floor. They have been coated with a thin outer layer of glauconite. The reason that the Upper Greensand, with its boulder bed, is of rather unusual facies here is probably because it was deposited on a residual Late Kimmerian swell or high, even though it is, of course, above the basal Gault (main Late Kimmerian) unconformity. It is an interesting condensed sequence and this ties in with the penecontemporaneous erosion (Drummond, 1970 ). For more recent information on the ending of the Cretaceous extensional phase see the petroleum geology literature.

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8.. UPPER GREENSAND continued:

8.2. Fossils (some)

Upper Greensand fossils

More Cretaceous  Fossil

Exogyra obliquata in Upper Greensand

Aquipecten aspera in Upper Greensand

Entolium in Upper Greensand

Robust marine fossils, like those shown above are common in the Upper Greensand. It has undergone some diagenesis and calcitic shells are preferentially preserved. Fossils such as Exogyra obliquata bivalves and serpulid worm tubes are common, although often at beach level good fossils have often been removed by collectors.

Ammonites had aragonitic shells and thus they can be present as either internal moulds of sandstone or more frequently as phosphate moulds in certain phosphatic, and usually more argillaceous, horizons.

Calcite-cemented glauconitic sandstone of the Exogyra Rock which occurs in the middle of the succession. This bed is conspicuous because it projects in the cliffs and contains large numbers of fossil shells, particularly Exogyra obliquata (Pulteney). In older literature this is referred to as Exogyra conica (J. Sowerby). Although elsewhere in Dorset it is almost 3 metres thick, in the Lulworth area it only about a metre It contains Pecten (scallop) bivalves of which a part is visible in the photograph. Small echinoids ( Caratomus, Salenia, Hyposalenia, Discoidea ) are fairly common in certain other exposures where there has not been too heavy collecting. This bed occurs near the entrance to Lulworth Cove but the easily accessible fossils have gone. You can look up, though, and see the Exogyra shells. There are three argillaceous beds above each of about a metre thickness, of which the top one is the Ammonite Bed (see Arkell, 1947, p. 190 for summary faunal list). Large nautili occur in the bed beneath it at some localities.

The bivalve Aequipecten aspera (Lamarck) (Pecten asper in older books) is a very common scallop (like the modern "sea-butterfly") of the Upper Greensand with Exogyra obliquata (Pulteney) and some other shell material including serpulid worm tubes Rotularia concava (J. Sowerby).

Entolium orbiculare (J. Sowerby), another common member of the Pecten family in the Upper Greensand. This small specimen (about 5 cm) is not perfect because the " ears " are not visible. Perhaps, this small scallop and Aequipecten asper were able to swim as many modern scallops do by flapping their valves and thus avoiding being buried in the sand. Relatives of this mollusc at the present day have a number of small eyes in the edge of the mantle, useful for these more active members of the Bivalvia.

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8. UPPER GREENSAND continued:

8.3. Bioturbation

Bioturbation with glauconitic sand in burrows, Upper Greensand, Lulworth Cove, Dorset, England

Bioturbation or burrows by organisms is best developed in sediments of shallow or fairly shallow, marine origin. The Upper Greensand is usually well-bioturbated. Burrows, probably made by crustaceans and worms, are common. At some localities particular types of burrow systems that form trace fossils can be identified. In the photograph here we see a vertical cross-section through various unidentified burrows, some of which are partially compacted. They are very clearly visible because dark glauconitic sand has filled the burrows which have been excavated in buff sand, now carbonate-cemented, which was relatively deficient in glauconite (I am using "glauconite" in a general sense here for simplicity - i.e. like "glaucony"). The exposure is a small one of about half a metre at the back of the beach next to the shingle, a short distance east of the beach cafe. It varies in quality from time to time depending on movement of the shingle by storms.

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8. UPPER GREENSAND continued:

8.4. Eastern Exposures

General view of the eastern exposure of the Albian, Gault and Upper Greensand, Lulworth Cove, Dorset, England

Eastern faulted junction of Upper Greensand and Chalk, Lulworth Cove, Dorset, England

Here is an interesting fault system at the contact between Upper Greensand and Lower Chalk at the eastern end of the Chalk section at the back of Lulworth Cove. To understand this fault see the table above of the classification of Lulworth area faults according to various authors.

Look at the rough Upper Greensand fault breccia towards the right. This passes down into in situ Upper Greensand. It very heterogeneous and shows little sign of brittle fracture. It is obviously earlier than the narrow and well-defined Chalk fault breccia on the left. It is too late, however, for typical Late Kimmerian (the mid-Cretaceous movements); it is post-Albian (after the Late Cretaceous Albian Age). Furthermore if the bedding is returned to a low angle, as it would be before the Tertiary (Alpine) movements, then the fault is too low-angle for extension (Late Kimmerian movements were mainly of extension). Thus, it seems likely that both fault breccias are Tertiary but perhaps formed under different compression regimes at different stages in the development of the Inversion.

With regard to the orientation of the fault plane and type of displacement, it seems to be an F5 on Arkell's classification. It hades northwards and the fault plane is at a steep angle. Bevan (1985) reclassified Arkell's F5 faults as antithetic [i.e. a minor, secondary fault, usually one of a set, whose sense of displacement is opposite to its associated major and synthetic faults]. Certainly the later chalk fault breccia shows brittle-fracture, it is sheared and almost monomict [of one rock type, as opposed to oligomict and polymict]. These features are compatible with a Tertiary antithetic origin, probably at a time of low-angle, maximum compressive stress.

A further problem in addition to those discussed above is that there is the reduction of dip northward, onto the hanging wall [the side of the fault to which the fault plane hades, or inclines from the vertical - thus this wall appears to hang. Opposite of footwall.] Why is this? The continuation of this fault also deserves thought. Where is it on the western side of the cove?

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9. CHALK (start):

9.1. Introduction

Chart for the Chalk of southern England relating older Chalk Zones to the modern lithostratigraphic schemes of Mortimore and the British Geological Survey

The Chalk at the back of Lulworth Cove is now considered. The strata are dealt with in the order in which they are encountered walking round the cove and not in stratigraphical order. Because the strata are steeply dipping northward, they young in a northward direction, and therefore the Chalk outcrop is at the northernmost of Lulworth Cove. The chart above gives the terminology of the Chalk in both old traditional terms and in new lithostratigraphic nomenclature of of Mortimore and of the British Geological Survey.

The Upper Cretaceous Chalk is very well-known as a fine grained coccolith limestone that is usually relatively soft. At Lulworth Cove only the Lower and parts of the Middle Chalk are seen. The Lower Chalk is greyer and harder than the typical white chalk and has a significant clay content. It is cyclical and does not contain flints. The Middle Chalk is rather harder and more nodular than elsewhere. All the Chalk in the Lulworth has been sheared to some extent by tectonic action and in the Durdle Door area the flint is fragmented into small pieces. The main Upper Chalk the White Chalk is not properly exposed in the cove but lies under Bindon Hill to the north. You can see it at other places such as Studland and the Isle of Wight.

The general stratigraphy, sedimentology and origin of the Chalk is not discussed here in detail. See the diagram above and also Gale and Kennedy (2002) in Smith and Batten's (2002) guide to Fossils of the Chalk. As they point out that the Chalk is distinctive and very widespread. Virtually identical Cretaceous deposits, with the same fossils, extend across northern Europe and into central Asia, and are found as distant as Texas and Western Australia. A type of unconsolidated chalk forms in the modern oceans from the rain of of calcareous plankton debris. In the Late Cretaceous, pelagic chalks spread from the more usual ocean environment onto the continental shelf and epicontinental seas of northern Europe as a result of a major rise in sea-level. Hundreds of metres of chalk formed a blanket-like cover over vast areas. Salinities were normal, and the sea floor was generally well-oxygenated. The sea floor was also below the limit of light penetration, and there is an absence of organisms that characterise shallow-water limestones that formed in the photic zone. At its maximum extent, the Chalk Sea probably covered all of the British Isles except the Scottish highlands (see Gale and Kennedy, 2002) for more information).

Some Chalk fossils are mentioned briefly in the following sections on the Chalk. For more information on Chalk fossils the reader should again refer to Smith and Batten (2002).

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9. CHALK continued:

9.2. Lower Chalk

Simplified diagram of the stratal succession in the Lulworth Cove area of Dorset, England

Albian (Upper Greensand) and Chalk divisions, zones and stages in Dorset, England

General lithostratigraphy of the Chalk of southern England

There are good exposures of Lower and Middle Chalk exposures at the back (north side) of Lulworth Cove. In the middle of the Chalk cliff, high above the beach, is the major east-west strike fault. It is shown in the geological map above and on the general cross-section.

Upper Greensand (Albian) junction with Cenomanian Chalk at Lulworth Cove, Dorset, England

Here is the junction, between the rather weathered (and therefore rather brownish in the photograph) Upper Greensand and the Chalk. The Chalk here has a Basement Bed with small phosphate nodules. They are mostly only one or two centimetres in length and of a light brown colour. Some of these have replaced fossils and occasionally a phosphatised ammonite may be visible.

Phosphate-rich beds usually form when there is very slow deposition and gradual accumulation of phosphate from organic remains such as debris of plankton. In fact, the base of the Chalk here does represent a hiatus (a pause in sedimentation - a gap in the time sequence), and this can be shown by the fossil content.

Above the Basement Bed the Lower Chalk, of Cenomanian Age, is cyclical with alternating beds of fairly pure chalk, without flints, and thinner, compacted beds of argillaceous (marly) chalk. They are better seen where they are washed by the sea, as at Man O' War Head between Dungy Head and Durdle Door.

Cenomanian cycles in the Lower Chalk at Lulworth Cove, Dorset, England

At beach level Lower and Middle Chalk are seen separated by the Plenus Marl and dip steeply northward. The Lower Chalk is cyclical, rather argillaceous and without flints. The Middle Chalk is nodular, without flints and forms the lower part of the cliffs at the back of the cove. The Upper Chalk is white chalk, rather harder than is usually case in England, and contains flints. It is only present in the upper part of the cliff north of the fault and is overturned to some extent.

The Lulworth Cove Chalk has been briefly described by C.W. Wright in Arkell (1947). The Basement Bed (see below for more details) is preserved immediately above the Albian as 0.91m (3 feet) of buff sandy chalk with a few phosphatic nodules and fossils.

Ater that distinctive and peculiar bed we encounter the main cyclical sequence of the Cenomanian or Lower Chalk. Wright ( in Arkell, 1947) commented that it is so faulted that only about 9.14m (30 feet) remain. In comparision it is about 27.43m (100 feet) at Worbarrow Bay and thicker still at Ballard Down, Swanage.

Is the reduction in thickness in the Lulworth area the result of strike faulting or of condensation or of both condensation and strike faulting? Bear in mind the proximity of the section to the main Inversion Fault (of F4 type) and the possibility that the exposure here is of Cenomanian Chalk between two strike faults at the margin of the Inversion (examine the House cross-section shown above). It is likely that both are involved.

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9. CHALK continued -

9.3.The Plenus Marl

The Plenus Marl  at the top of the Lower Chalk, seen in the eastern outcrop of the back of Lulworth Cove, Dorset, England, 1997

The Plenus Marl and the Upper Greensand - Lower Chalk junction at the eastern outcrop of the back of Lulworth Cove, Dorset, seen on 14 Nov 2005 after the storm of 3 Nov 2005.

These pictures above are given as illustrations of the Plenus Marl at the eastern exposure. Notice that, in addition, comparison between the photographs reveals that the action of the 3 November 2005 storm seems to remove the chalk talus, leaving mostly the flint pebbles. It has also resulted in a small fresh cliff at the base of the main and old cliff. This particular storm sadly caused the deaths of two boys who were washed away by the large waves actually entering the cove. Perhaps this storm has initiated a new phase of erosion and undercutting within Lulworth Cove.

Sheared Plenus Marl at the west side of the promontory of Durdle Door, near Lulworth Cove, Dorset, 2005.

Guard of the belemnite Actinocamax Plenus of the Plenus Marl, Chalk, Dover

The upper limit of the Lower Chalk is marked by the Plenus Marl, a grey marl, much softer than the adjacent chalk and breaking into small angular fragments. It is very easy to recognise. At the present time there is a well-developed beach at the back of Lulworth Cove. A result of this and of the protection afforded by the narrowness of the inlet to the cove is that the erosion of the Chalk is limited and slow. Thus the Plenus Marl is not normally seen at Lulworth Cove in a fresh and clean exposure. I have added a photograph of the same bed on the west side of Durdle Door where it is eroded clean by the sea, but is highly sheared.

The Plenus Marl at Lulworth Cove is about 1.83m (6 feet) thick. The characteristic belemnite is Actinocamax plenus, although this fossil is not easy to find. The Plenus Marl is a well-known and widespread marker horizon and is the subject of many papers. It is important because it is linked to evidence of a palaoeoceanograph perturbation. In Gubbio in northern Italy its equivalent is a one-metre thick dark bank of organic-rich shale and radiolarian sands known as the 'livello Bonarelli'. It is interesting that the Bonarelli horizon has a pronounced positive shift in delta 13C (the isotope of carbon). This peak can be identified in Plenus Marls of East Kent. See

In terms of zones and stages there has been some argument about the position of the Plenus Marl. Kennedy (1970) classified as Cenomanian-Turonian and assigned the lower part to the zone of Metoicoceras geslinianum and the upper to the zone of Metoicoceras gourdoni. Skelton (2003) for more information on this.

Some useful details, with a faunal list, have been given by Jefferies (1963) of the plenus Marl at Durdle Door: "North-east corner of Durdle Cove at foot of cliff. Fig. 10. 30/805803. Despite great regional tectonic disturbance the plenus Subzone seems complete. Base Bed 1 abrupt. No 2b or 3a. Bed 8 consists of 8a, band c. Aragonitic fauna abundant in Bed 1 (highly exceptional) as well as in Beds 2-3 and 4-8. Characteristic fossils: Bed 1, large Ostrea vesicularis, Neithea quinquecostata; 2, Entolium membranaceum (c), Calliderma smithiae; 3, Metoicoceras geslinianum; 4, Actinocamax plenus, Oxytoma seminudum; 5, Sciponoceras sp., Metoicoceras gourdoni." It is very interesting that an aragonitic fauna has been preserved in Bed 1. In most of the Chalk the aragonitic fossils have been dissolved so that only the calcitic fauna is visible. I do not know whether the aragonitic bed is preserved at Lulworth Cove.

For information on the palaeoecology of the Plenus Marl, with emphasis on a section at Merstham in Surrey see also Jefferies (1961).

Chalk fossils

More Cretaceous  Fossil

For more on the Chalk and Chalk fossils see: British Chalk Fossils - by Robert Randall.

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9. CHALK continued:

9.4. Middle Chalk or Holywell Chalk Formation

Simplified diagram of the stratal succession in the Lulworth Cove area of Dorset, England

The Turonian (Middle Chalk, excluding the Holaster planus Zone at the top) is seen at the base of the cliff at the back of the cove where the chalk is in the Inoceramus labiatus Zone. Characteristic fossils have been obtained. They include a single specimen of Cardiaster pygmaeus Forbes. Rowe (1902) recorded "Ammonites cunningtoni (?= Prionotropis woollgari Mantell sp.) and sometimes worn ammonites are visible in situ. The present author has seen a large specimen collected from the central part of the back of the cove. Wright mentioned that it is sometimes possible to reach a face of the Terebratulina lata Zone by climbing up the talus. This is not recommended.

The common bivalve  - Mytiloides labiatus, in the Middle Chalk of Lulworth Cove, Dorset, England

At the back of the cove look for a Middle Chalk zone fossil, the bivalve - Mytiloides labiatus Schlotheim. This was formerly known as Inoceramus labiatus von Schlotheim, 1813 and the name Inoceramus labiatus has been widely used in the older literature; from this species the I. labiatus Zone takes its name. In the USA the similar Inoceramid known as Mytiloides mytiloides is common in the Upper Cretaceous (see Cobban, 1983). See Cleevely and Morris (2002) for more information on Inoceramid taxonomy.

The Inoceramids are very interesting because they had a prismatic calcite layer of the shell which is preserved in the British Chalk. Aragonitic shells have been lost in most of the Chalk so quite a distorted impression of the original benthic fauna is given by the cliff exposures. There would have been many aragonitic bivalves and other organisms of which there is no record. Gale and Kennedy, 2002) commented that the aragonitic shells probably dissolved on the sea floor or just below it and that typical White Chalk faunas, dominated by originally calcitic organisms are 'preservation faunas' in which the aragonite component has been lost. Of course, it should be noted that aragonite is usually lost in permeable limestones through which meteoric water can percolate, and thus some later loss is possible (c.f. Portland Stone). Aragonitic layers of the Inoceramids have been lost but the prismatic calcite is more resistant to dissolution. Inoceramid prism are common throughout the Chalk even where near-complete fossils are not preserved. They are quite conspicuous in thin-section.

Although they are not usually preserved in the Middle Chalk, a mould of a large ammonite has been found near this part of the cliff some years ago (by Dr Page).

Cretaceous echinoids

Because of sea erosion and extensive collection this is not a locality at which to find echinoids easily. Eroded specimens might just be found, so some examples of Chalk and other Cretaceous echinoids are shown here. Echinoids in the Chalk are important in showing that the sea was not very deep, certainly not too deep for this benthic and burrowing fauna. This distinguishes the coccolith ooze of the Chalk from the coccolith oozes which form in deep oceans.

For more on the Chalk and Chalk fossils see the webpage: British Chalk Fossils - by Robert Randall.

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9. CHALK continued:

9.5. The Black Rocks, Rock-Fall Locality

Black Rocks and the apparent source area in the cliffs above the major fault, Lulworth Cove, Dorset, 29th September 2012

At the Black Rocks, algal coated boulders that have fallen from the cliffs at Lulworth Cove, Dorset, seen on the 29th September 2012

Low spring tide at Black Rocks, Lulworth Cove, Dorset, showing Chalk and Wealden cliffs

view of the cliff with the Black Rocks

The Black Rocks

Accident at Black Rocks, Lulworth Cove, Dorset in July 1957

Fall of a

Bedding planes and shears in the Upper Chalk above Black Rocks, Lulworth Cove, Dorset, October 2005

At the back of Lulworth Cove, towards the western side and not far from the access to the beach and the cafe are the Black Rocks. As you can see they are actually not black but green with algae, although appearing dark from a boat. These rocks only occur at this one place and yet the Chalk cliff has broadly the same strata and structure along its east-west length.

Although little seems to have come down recently, at distant intervals of time it seems that some debris falls from the scar providing new boulders for the Black Rocks. The accident in 1957 happened when a heavy boulder fell almost vertically from about 30 m (about 100 feet) up and then impacting on the lower part of the cliff with high velocity, disintegrated explosively in part with a loud bang, the "shrapnel" causing injuries to sunbathers ( Anonymous, 1957 ). The remaining lump bounced into the sea but, fortunately, no-one was killed. Fortunately, such falls are very rare so the risk of walking past the site is usually very small.

The great inversion fault in the Chalk cliffs of Lulworth Cove, Dorset, England

Photographs here show the suggested location of the source of the Black Rock boulders, but even if this is correct there are many interesting problems. Wright (in Arkell, 1947) referred to the occurrence on the beach of boulders from the Holaster planus zone, now the Sternotaxis planus Zone of the Lewes Nodular Chalk. These strata are from the lowest part of the Upper Chalk. He was probably referring to the Black Rocks. The boulders can be seen at low tide and they consist of fairly hard chalk containing flints. They are large enough not to move easily on the beach and thus they are coated to some extent with dark green, marine algae, giving at a distance a black appearance.

The flinty chalk of the boulders contrast with the flint-less Lower and Middle Chalk in the cliff. They seem to have fallen from the higher part of obvious scar seen in the photograph above the outcrop of the Arkell's F4 (steep south dipping) fault. This is actually the great fault of the English Channel Inversion Structure, and is the most important fault in the region. The exact position of the faults is not placed with certainty in the image, because the cliff is partly grassed over. As can be seen on a geological map above, at this point the fault shows some curvature and trends into the cliff at the west side of the scar.

Overturned Upper Chalk, high in the cliffs above Black Rock, Lulworth Cove, Dorset

In the photograph above observe the overturned Upper Chalk, probably from the Sternotaxus planus Zone (Lewes Nodular Chalk) north of the F4 fault high in the cliffs above Black Rocks.

Some questions arise.

1. Was there at one stage a large fan of fallen talus with the boulders on the outer, seaward side? No fan of talus remains. Alternatively, have the boulders fallen individually and bounced out from the cliff, as in the 1957 incident?

2. Why was a fall of Upper Chalk only here? It occurs most of the way along the middle to upper part of the Chalk cliff.

3. Did the original fall, have any connection with neotectonics [recent movement on faults]? It seems unlikely but some small movement on this fault could have destabilised the adjacent cliff. The fault is one of the largest in southern England, it marks the boundary of the English Channel Inversion and is connected to a deep basement structure. (Incidently, in the Purbeck Unio Bed of Stair Hole you can see the evidence of earthquake liquifaction associated with a Late Kimmerian precursor of this fault. There have been earthquakes here but it was a very long time ago.)

4. Look at extent of vegetation on the cliff, the extent of scars from falls, the extent of undercutting by the sea. Think about "global warming", sea-level changes. Is the present time a phase one of rapid erosion or is it perhaps a phase of slow erosion, with more rapid erosion to come in the future?

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9. CHALK continued:

9.6. Black Rocks, Rock Fall, Locality - More Information

Another accident took place here in 2009 and again, fortunately no-one was killed. Here is an extract from a press report (Steven Smith, 2009).

"Nine-year-old boy who was buried by rocks at Lulworth Cove is discharged.

8:10am Tuesday 22nd September 2009 in News By Steven Smith

Danger: Lulworth Cove was the scene of a horrific accident on Sunday, when a cliff fall (location marked by asterisk [Black Rocks area]) buried alive a boy of nine. [This was a rock fall from about 10ft (3m.) above and not from the high Black Rocks sourc site high in the cliffs.]

The nine-year-old boy thought to have been seriously injured when he was buried under rocks was discharged from hospital yesterday, Coastguards said. He was completely covered by the falling rubble on Sunday as he played in the late summer sun at Lulworth Cove. Initially it was thought that the child had serious spinal injuries, but yesterday he was discharged from hospital, a Coastguard spokesman confirmed. He said: "It's all round good news, if you consider the situation. It's an unpredictable event of being in the wrong place at the wrong time; it had a very successful outcome."

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9.7. Chalk Cliffs - Future Rock Fall Risk - General

The back Chalk cliff of Lulworth Cove, Dorset, seen obliquely from the eastern ascent path, 18th November 2012, - generally stable in the upper part at that date

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10. STRUCTURE (start):

10.1. Introduction to the English Channel Inversion Structure

The major east-west fault in the Chalk of Lulworth Cove, Dorset, separating overturned Chalk from north-dipping Chalk, 18th November 2012

The most important tectonic structure at Lulworth Cove is shown above. It is strangely common for visitors to the cove to look at the minor structures of Stair Hole and to almost ignore this, the great boundary fault of the English Channel Inversion Structure! This is the main structural feature of Lulworth Cove - consider its origin.

Cross-section of the northern margin of the English Channel Inversion Stucture at Lulworth Cove and its relationship to the Wytch Farm Oilfield

The diagram above is just a simple cartoon for educational purposes, and does not show the numerous faults or other details. See accurate and technical cross-sections for details. The key work on this subject is the impressive seismic study of Underhill and Paterson (1998) - Genesis of tectonic inversion structures: seismic evidence for the development of key structures along the Purbeck - Isle of Wight Disturbance, Journal of the Geological Society, London, vol. 155. This paper provides various accurate sections through the Purbeck Disturbance, and is essential reading. This new evidence is consistent with the better of the older views, but eliminates some unsatisfactory hypotheses. The many diagrams cannot be reproduced here, so the paper must be obtained by anyone studying the area seriously. See also the related work of Underhill and Stoneley (1998).

Lulworth Cove, Dorset in relationship to the Portland-Wight Basin or English Channel Inversion

Geological cross-section through Lulworth Cove, Dorset, a simplified version by Ian West

The section above is a very simplified and diagrammatic cross-section to explain the main features without showing the details. It is intended for basic educational rather than technical purposes.

Hypothetical section through Lulworth Cove, Dorset, modified after one by the late Professor Michael House, based in turn on the work of previous authors

The great inversion fault in the Chalk cliffs of Lulworth Cove, Dorset, England

Overturned Upper Chalk, high in the cliffs above Black Rock, Lulworth Cove, Dorset. In the footwall of the inversion fault.

Above are given a diagrammatic geological cross-section through strata and faults of Lulworth Cove. The simplified version incorporates aspects of cross-sections of West (1964), Bevan (1985) and House (1989) but with modifications. This is intended to be merely illustrative of the general structure, rather than being the best calculated cross-section. It can be considered in different ways, either as a simple hypothetical explanation of the structures or a simple basic model for modification.

A modified version of a very good cross-section by House follows. This is more accurate in that it shows more faults, but it does not deal with the Lulworth Crumples.

To introduce the cross-sections, it is initially quite clear from geological maps and the cliff exposures that that the Chalk is folded so as to produce the Purbeck Monocline. This is a very asymmetrical anticline with a steep north limb and a very gentle south limb bringing the Chalk down to the sea-floor nearly 30 kilometres to the south (a long way south of the Isle of Portland). Note that the fold in the Chalk has a very acute foresyncline (the sharp bend at the base). Note also that there is an unconformity under the Chalk, Upper Greensand and Gault. That is to say, the Jurassic strata underneath are not parallel but were folded before the Chalk was deposited. Note also that the fold is situated over a fault, and this is believed to have originated as a thrust fault in Upper Palaeozoic strata at depth during the Hercynian Orogeny (Carbo-Permian - round about 300 million years ago).

Of major importance both academically and economically (because it is the reason for the existence of the Wytch Farm oilfield) was the Late Kimmerian phase of extension. This (named after the Crimea where is it well shown) was connected with the break-up of the supercontinent Pangaea and the development of the North Atlantic. Although there was some similar early movement, the Late Kimmerian was the Late Jurassic to Early Cretaceous phase of this. In Dorset there was a stretching effect as the ocean started opening to the west. Dorset, including Lulworth Cove, was still an outlying eastern area off Newfoundland at the time (only about 1000 km from the present North America), but beginning to pull away to the east. The English Channel Basin or Channel Inversion, and the strata of the southern part of Lulworth Cove, was thus formed off the western coast of America and has now drifted a long way eastward.

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10. STRUCTURE continued:

10.2a. Inversion Structure - Modelling

See the very interesting modelling of an Inversion Structure on Utube by Philip Prince. This is particularly good at representing the northern margin of the English Channel Inversion at Lulworth Cove.

Modelling of an Inversion Structure.

Look at the striking similarities to the northern margin of the English Channel Inversion at Lulworth Cove. These are very striking!

Bear in mind, though, that the English Channel Inversion Structure is a re-activated Variscan (Hercynian) structure. It was, of course, compressional in the Carbo-Permian, with major thrust faults of the type that are seen at the surface in the southern Mendip Hills at the present. During the extensional phase of Inversion Structure, displacement on the major faults was listric. Consider the compressional phase with this background structure (i.e. some reversal of movement direction on the old listric faults). These are technical aspects that are complications on a basic pattern. The model shown by Prince makes it possible to visualise the main scheme and possible variations on it. It is very useful and requires study to look for similarities and differences. Go to this Utube site is strongly recommended.

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10. STRUCTURE continued:

10.2. Fault Systems

The Lulworth area is an excellent area for the study of faults. Normal (extensional) and reversed (compressional) faults in horizontal or nearly horizontal strata and simple thrust faults are easily understood. However, the there are some interesting complications that are present in the Lulworth area and which should be borne in mind.

1. The strata is generally steep dipping and in some cases overturned.
2. Here a major fold is also faulted, and in fact, related in origin to a history of major faulting.
3. The faulting is often of growth faulting type [faulting in which movement has take place during sedimentation, and thus having thickness differences across the faults].
4. There are two main ages of faults, although this is a simplification. Later faulting, the most obvious, is usually compressional Tertiary (Alpine) but there has been earlier Late Cimmerian movement (or Late Kimmerian). This was a phase of faulting of Late Jurassic - Early Cretaceous age, named because of its occurrence in the Crimea. In this area it is dominantly extensional - i.e. normal.
5. Other problems involve three-dimensional variation, the intersection of faults, the plunge of the folding, the relationship of folding dates to faulting dates etc.

The interpretation of the faults in the field is not easy because of limited exposures. However, there is better understanding now because of seismic data relating to petroleum geology. Boreholes and offshore investigations have helped.

To simplify the matter of faulting in the Lulworth area, the standard classification of faults used here is given. Interpretations vary. The paper of Bevan (1985) is useful. (A problem of non-compatibility with the old work of Phillips (1964) means that caution exercised in interpreting the Lulworth Crumples of Stair Hole in Phillips' terms.)

Classification of faults in the Lulworth Cove area, Dorset, according to Arkell, Phillips and Bevan - summary diagram

The most important faults are emphasised. At Lulworth Cove it is best to concentrate on the macrofaults, the large faults. The F4 is most important. The antithetic F5 faults are interesting but may sometimes break the rules and not be normal.

For mesofaults (shears etc) examine the Chalk particularly at St. Oswald's Bay and to the Durdle Door area. Man O'War Head is excellent for study of faults.

The broad theme of faulting in the Lulworth Cove area is, as noted above, the Late Cimmerian extensional faulting within the Jurassic and Cretaceous. The major ones were re-activations of old Hercynian thrust planes, originally compressional, of course, and at some depth under the area. The thrust planes were effectively pulled apart as normal faults, probably often listric [curved].

As mentioned above, the faulting was of growth type. It developed during sedimentation with a long phase of small earthquakes and depression of the downthrow side. This allows increased sediment accumulation on the downthrow, and therefore greater thicknesses of Jurassic and Lower Cretaceous deposits. This is needed to obtain the necessary burial depths for oil generation from the source rocks (about 3 km giving a temperature of about 100 degrees C). So the growth faulting related to the greater subsidence of the English Channel (offshore) basin.

Much later in the Oligocene to Miocene, Europe was affected by a new phase of stress, the Alpine Orogeny. This was the (second) northward impact of the African Plate. Dorset was by now well-separated from America by the growing North Atlantic. Although quite far north from the orogenic belt (the Alps and Pyrenees etc) it was subject to compressive stresses from the south. These stresses were conveyed through the deep basement and had the drastic effect of reversing the sense of movement on the faults. The normal faults now became reversed faults. The basin was now "inverted" (i.e. the direction of vertical movement was reversed). The former basin now became the English Channel Inversion, a raised structure, a high.

For simplicity, the major fault on the cross-section of Lulworth Cove is referred to as the "main inversion fault". This is because it is the northern boundary fault of the English Channel Inversion. The direction of movement on the fault has reversed from Jurassic-Cretaceous downthrow on the south side to Tertiary downthrown north. This is shown on the diagrams.

Before the recent petroleum geological studies of the area and particularly before the accumulation of seismic data, the structures at Lulworth Cove were misunderstood. Emphasis used to be on the Purbeck Monocline. There is, of course, a fold as shown on the sections and it is quite important. The fold, however, is not the primary structure. To some extent, it is a drape structure over a fault. It is not merely a drape though; the steep limb has been subjected to intense compression from the south with consequent thinning of the near-vertical strata.

In addition there are various complications. One of these is the easterly plunge of the monocline. Its importance is that the deep area of the steep limb, near the foresyncline, is brought up to a higher level at Durdle Door. Thus it is there that the most intense compressional structures are accessible and visible.

To follow these topics further see the papers of Underhill and other petroleum geology and structural studies.

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10. STRUCTURE continued:

10.3. Lulworth Cove Geological Cross-Sections

Reading of the older publications of Arkell (1938; 1947), West (1964), Phillips (1964), Bevan (1985), Selley and Stonely (1987), Penn et al. (1987) and House (1989) is recommended to consider some of the various views on this much visited structure. Many theories have been put forward and various ones have involved substantial thrusting, gravity folding, drag folding, collapse, rollover anticlines, and inversion. Recent petroleum exploration will have advanced knowledge of the structures in this area appreciably.

Attention is drawn to some of the many disputable points. This is only a limited discussion and the matters can be followed much further in the literature. There is the problems of compression; "gaping" ; and the Lulworth Crumples and the other crumples. Sir Aubrey Strahan, about 100 years ago was perceptive on this. He said in 1898, referring to the lower part of the fold at Lulworth Cove that "Here, therefore is indicated a region of compression. Upwards .. the rapid divergence of the two groups (Wealden and Lower Purbeck) points to a region in the monocline where there was a tendency to gape." Strahan then suggested that you take a paper-book or a thin journal and fold it into an S. Observe the gape at the top. This seems very unscientific now but it should be noted that Bevan (1985) found Sigma One to be nearly horizontal in the Chalk of the steep zone of the Purbeck Monocline (Bevan, 1985, fig. 3, p. 340). He argued, though, for a different explanation. He suggested layer parallel extension during draping over reactivated Jurassic growth faults during N-S shortening.

Lulworth Crumple in Purbeck strata in the cliff near East Over, Lulworth Cove, Dorset

The Lulworth Crumples, one of which is shown here, are small folds always in the Middle and Upper Purbeck strata and within the north limb of the major monocline. They are usually asymmetrical folds or overfolds of some type and plunge down to the east at a small angle. Similar crumples occur at Blashenwell near Kingston, at Herston near Swanageand are well-exposed at Peveril Point in Durlston Bay. They are shown diagrammatically in the diagram and attributed here to (disharmonic) movement of incompetent Wealden strata at the contact with the more competent Purbeck Group. If the Wealden sediments moved to some extent towards the inclined axial plane (the area of "gaping" "), the directions of vergence of the small folds is explained. Bed-over-bed drag effects would add to the effects at the base of the Wealden and compensate at the top. Thus, there are no crumples in the Gault and Greensand (West, 1964). Other interpretation of the crumples have involved collapse (Phillips, 1964) or gravity movement (Lees in Phillips, 1964)(if there was space at this low level for the material to slump into!)

Another disputable point is how many faults are there in the fold. I simplified the diagram and have shown one. Bevan (1985) has shown two and a possible minor branch. House (1989) has shown three. Some early interpretations (Strahan, 1898) showed one and those of intermediate date none. There does not seem to be much disagreement at present that at least one major south-dipping fault lies beneath the monocline. The major fault in the Chalk at the back of Lulworth Cove is believed to be the continuation of it (as shown in the diagram here). The regional plunge of structures down to the east results in a low-level view of related structures further west where faults are clearly seen (Abbotsbury-Ridgeway Fault system - see House, 1989, fig 22 and references to earlier work).

Another problem is that of whether or not there is a rollover anticline in the pre-Gault strata. Selley and Stoneley (1987) have argued for one; Penn et al. have argued against. I have simplified the section here and (unlike House, 1969) have omitted a rollover from this diagram. Without it the diagram not only explains Lulworth Cove but also the sections further east. Plunge of the fold down to the east means that Worbarrow Bay represents part of the " gaping " region with thick Wealden. Other factors, however, are involved in Wealden thickness changes that I will not discuss fully here. One of these is that the present coast is oblique to the north limit of the inversion in basin sedimentation terms and thus localities from Worbarrow to Durlston are actually in the inversion and, therefore, units there have greater thicknesses.

Yet another complication is that the diagram generally does not show thickness changes within the formations. This is a further simplification here . The only one shown is the thinning of the Purbeck Group in the compression zone, as seen in the Durdle Door area (the upper part of the Purbeck is lost by strike faulting).

Also see House (1969) for consideration of borehole data from the area to the north of Lulworth Cove.

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10. STRUCTURE continued:

10.4. Structural Locations at Lulworth Cove

A variety of the locations within Lulworth Cove that shown particular structural features of interest are shown below in a series of photographs. These are from different dates and vary in quality.

West Horn of Lulworth Cove

Chalk of the northern part of Lulworth Cove, Dorset, in 2002

Northeastern part of Lulworth Cove

East Horn of Lulworth Cove

The steeply-dipping Unio Bed, west side of Lulworth Cove, Dorset, with Southampton University students, October 2011

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11. GEOMORPHOLOGY (start):

11.1. Geomorphology - General

For a discussion of the geomorphology of the Lulworth Cove area see Goudie and Brunsden (1997).

Geological Map of the Isle of Purbeck - simplified This simplified geological map of the Isle of Purbeck shows Lulworth Cove, just beyond the limits of the " island " (limit is Luckford Lake and Arish Mell in Worbarrow Bay). Before considering the details of the Lulworth area it is intended to place the geological outcrop in broad perspective. The relatively harder, less easily eroded rocks are shown cross-hatched. Note the narrow steep-dipping Chalk outcrop forming the ridge of Purbeck Hills and also note the upland of Portland and Purbeck stone in the south. Between these two sets of hills is a valley of Wealden sand and clays. This Wealden valley is very wide at Swanage in the east and extremely narrow in the Lulworth area. A steep dip, a thinner Wealden succession and some strike faulting are the major reasons for the narrow outcrop in the west.

This simplified map does not show the full details or the cross-sections. The reader needing further information should see the British Geological Survey 1:50,000 geological map - Swanage, Sheet 343 and 342. This map covers much the same area as the diagrammatic map given here and includes Lulworth Cove and Durdle Door. Some more specialist readers may wish to see the area in terms of both onshore and offshore geology (not shown on the map here). For this consult British Geological Survey 1:250,000 Series, Portland Map, Sheet 50 degrees N. -0.4 degrees W. This includes Lulworth Cove but is on a smaller scale and more complex. It does, however, include an enlargement of the area south of the cove which is based on the work of Donovan and Stride (1961).

Evolution of the coast by formation of coves

The theory that the coast west of Lulworth Cove was developed as a series of coves similar to Lulworth Cove. The southern barrier was the Portland and Purbeck stone. Breaches in these steeply dipping rocks led to the erosion of the Wealden behind in several cases. The Chalk at the back was eroded at a much slower rate and thus became effectively another barrier. The coves, so formed linked up, leaving as a relic - the Durdle Door promontory, each side of which resembles the horns of Lulworth Cove, and finally outlying rocks like the Cow, the Blind Cow, the Bull and Man O' War Rock. This diagram is based on one of Calkin (1968), with minor modifications.

Evolution of the coast by formation of coves

Details in the western part - Durdle Door to Bats Head and the Cow rock.

Control of cove size by geological structure

This is a simple theoretical model of the manner in which cove size is controlled by the dip, and therefore outcrop width, of the Portland-Purbeck barrier limestone and the outcrop width of the Wealden which is controlled by thickness in addition to dip angle. Early views on these controlling factors were given by Arkell (1938). Since then there has been much more discussion about the Wealden Group.

Consider whether this simple theory is correct? If you study the topographic map you will begin to see some complications. One point which has been the subject of some dispute is that Lulworth Cove is clearly connected with a former stream valley running out to sea through the Portland and Purbeck barrier. Water flows down the valley near the cove but much of the valley system is dry now. The upper valleys are typical dry chalk valleys that have been cut in the Pleistocene at times of periglacial conditions when water flowed on the surface of frozen soil. We can see typical solifluction deposits of this type in a similar valley at Scratchy Bottom, west of Durdle Door.

When you examine the topographic map note whether all these postulated former coves at the sites of former stream valleys? Is the multiple cove theory really the correct explanation for the evolution of the coast here? Does Bacon Hole (SY 840797) and Chapmans Pool (SY 955770) and Pondfield Cove (SY 871796) fit into this theory?

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11. GEOMORPHOLOGY continued:

11.2. Loss of Beach Material and Increase in Erosion - 2011.

Reduced beach width at the back of Lulworth Cove, Dorset, on the 1st October 2011

Wealden exposure and erosion in front of the beach cafe at Lulworth Cove, Dorset, October 2011

The beach on the east side of Lulworth Cove, Dorset, seems to have been lowered recently, as shown by iron-cemented beach pebbles, 11th October 2011

Changes have taken place fairly recently at the base of the Chalk Cliffs at the back of Lulworth Cove. On the 1st October 2011, it was noted that the beach in the northwestern part seems to have lost most of the beach pebbles. At high tide it was not as simple as previously to walk past the cafe on the beach just to the east of the ramp. This is unusual. Some undercutting by the sea seems to have taken place in this area. Mud in the sea, visible in photographs above, shows that the Wealden clays on the beach are being eroded. This is also shown by siderite nodules projecting on the shore just here. At the eastern side of the cove, as shown in a photograph above, beach pebbles cemented by iron oxides seem to indicate that the storm beach level has recently been lowered.

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11. GEOMORPHOLOGY continued:

11.3. Chalk Cliff Falls, including 2011, 2012 and Onwards

Towards the eastern end of the Chalk cliff at the back of Lulworth Cove there are the sloping and grassed-over remains of very large chalk rock fall of long ago. See (above) old photographs above showing white chalk cliffs at the back of Lulworth Cove, rather than the present grassed-over slopes. Now some re-activation is appearing. This might cause some increase in risk to holiday-makers sitting at the foot of the cliff in this area. However, the last incident seems to have been in 2009 and it was not here, but at Black Rocks.

Old picture of Lulworth Cove, Dorset, probably from the 1950s, and showing a major Chalk cliff fall towards the north-east of the Cove

A general view of the back Chalk cliff of Lulworth Cove, Dorset, seen from the shore near Pepler's Point and the Eastern Horn, 29th September 2012, showing the major east-west fault

A view of a minor chalk debris fall at Lulworth Cove, Dorset, seen from the shore near the Eastern Horn, 29th September 2012

A small but new rock fall of Chalk debris at the back of Lulworth Cove, Dorset, as seen on 1st October 2011

A small fall of chalk debris at the back of Lulworth Cove, eastern part,  Dorset, 1st October 2011

It was noticed that in the back Chalk cliffs of Lulworth Cove, at this date, there has been some renewed erosion. There have been four minor cliff falls of chalk debris. None of these was major and all were smaller than cliff falls which have taken place recently at Lyme Regis. The falls at the present time seem to be small and limited and effectively the result of some cliff retreat which has reactivated the bases of old debris cones. However, it is a new development and worthy of observation.

A distant view of renewed chalk debris falls at Lulworth Cove, Dorset, seen from the shore near the Eastern Horn, 29th September 2012

Part of the back Chalk cliff of Lulworth Cove, Dorset, see on the 27th March 2014, after severe winter storms in January and February 2014


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11. GEOMORPHOLOGY continued:

11.4. Another Lulworth Cove?

Sunset Bay near Coos, Oregon, the Lulworth Cove of the USA

The general geomorphological features of Lulworth Cove are not unique. Near Coos on the Oregon coast is Sunset Bay, another "Lulworth Cove", with several similarities and some differences. It is a small circular bay with landward-dipping Eocene clays and weak sandstones (like the Wealden) eroded out. The horns are, like Lulworth Cove, of landward-dipping harder and more resistant rock, but in this case are of sandstone of the Eocene Coaledo Formation. Like the true Lulworth Cove a small stream enters the cove, partly to one side. Waves are refracted on entering the bay, and there is a quiet low energy beach at the back of the cove. Whereas Lulworth Cove faces the open sea to the south, Sunset Bay faces the Pacific Ocean to the west.

(For more information on this and for an aerial photograph (on p. 199) see: Lund, E. H., 2001 (originally 1973). Landforms along the coast of southern Coos County, Oregon. The Ore Bin (a monthly journal), vol. 35, No.12, December 1973. Originally published by the State of Oregon, Department of Geology and Mineral Industries, 1069 State Office Bldg, Portland, Oregon, 97201. Historical publication reprinted in June 2001 by Friends of Shores Acres, Inc., Coos Bay, Oregon, and on sale for 2 dollars, 50 cents at the gift shop at the Shore Acres Park, a coastal site worth visiting, near Coos, Oregon. See also: Moore, E. J. 2000. Fossil Shells from Western Oregon: A Guide to Identification. Chintimini Press, Corvallis, Oregon, 131 pp. Sunset Bay is discussed on p. 113 et seq.)

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11. GEOMORPHOLOGY continued:

11.5. Additional Problems

This section is a type of open-ended exercise. Some questions are put. Answers are not given, even if they are available. It is intentionally not referenced so that it can be used for projects or dissertations without being too easy.

1. First note that a higher raised beach of Hoxnian or of earlier Boxgrove raised beach is missing in East Dorset, although it ought to be found at round about 30 metres above sea-level. Therefore, an earlier phase of marine erosion is not well understood.

During the last Interglacial, the Ipswichian, about 130 thousand years ago, the ice had melted and sea level was a few metres higher than at present. The Portland Bill Raised Beaches at the end of Portland have been dated as 125,000 and 210,00 BP. If these dates are correct the younger of these would be about Ipswichian. The trend of these raised beaches is northeast - directly in the direction of the Fossil Forest. This would not be very significant, as it would be unlikely, of course, that the beach was straight but for the fact that the Budleigh Salterton quartzites (conspicuous liver-coloured pebbles derived from the Triassic Budleigh Salterton pebble bed in Devon) occur on the shore in Lulworth Cove. Did the Portland Raised Beach end near Lulworth Cove? The Fossil Forest Ledge is at about the height of the Portland Raised Beach but there is no obvious evidence that it was the cliff of raised beach. It is probably mainly the result of recent storm erosion. It is not possible to eliminate the possibility that the Budleigh Salterton pebbles have reached Lulworth Cove by some means such as ship ballast, although this is unlikely. They might have arrived here by some other geological means, such as debris in a solution pipe.

Examine the geological maps. Note the position of the Portland raised beach. Study the sea-floor geology. Consider the prevailing wind direction. Note particularly the offshore Portland Stone outcrop. From this perhaps the approximate original outline of the coast could be deduced.

One problem is whether there was a predecessor of the Chesil Beach. We need to consider this because what is now Portland Harbour (originally Portland Roads) was a possible route of Ipswichian sea entry into the area. The Isle of Portland provides evidence in its periglacial debris for an appreciably greater height at that time. The present "island" is only a relic of a larger southern Portland outcrop now under the sea.

Following this, the question arises what was the situation in the Devensian (last glacial)? The English Channel was dry but where did the local streams extend to? What sort of erosion occurred? Was there a river channel through the Portland outcrop (now under the sea) to the south or was the main channel under the Chesil Beach.

Now consider the Flandrian Transgression. This was the rise in sea-level from about 140 metres down to the present level within about the last 10,000 years. It was initially fast and later slower.

Another curious feature of the cove requires attention. The stream valley meets the cove at almost the same level (it is slightly above the beach). It is not drowned as an estuary, and it is not truncated as at Scratchy Bottom. Note that although it shows a little rejuvenation by cliff retreat, this is not on the scale of the streams at Chapmans Pool or Kimmeridge.

A guide to the geomorphology of the area by Goudie and Brunsden (1997) contains some interesting comments relevant to this topic. They comment as follows: : "It is not known how the development of the coast was affected by the high sea-levels of the last interglacial which formed the Portland raised beaches between 9-15m OD. There are beaches at the mouth of Lulworth and Stair Hole at this height and so the sea may have flooded the area. There is a notch above the Lulworth ice cream cafe at the same height but it is not known if this is of marine origin."

Perhaps there is a good indication here to a local source of the Budleigh Salterton pebbles?

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11. GEOMORPHOLOGY continued:

11.6. Wave Action

Wave action in Lulworth Cove, Dorset, 30 Dec 2005, shaped wave

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There have probably been various studies of clay mineralogy in different, specific strata that are present at Lulworth Cove. There is a wide variety of strata of different ages from late Jurassic to late Cretaceous. These strata have different types of clay mineralogy. A convenient summary has been made by I.F. Holmes (about 1975)- Clay Mineralogy of Purbeck and Wealden of Lulworth Cove. 14pp., Undergraduate project report. From knowledge of other studies in the region, this appears to be a good summary account with reliable conclusions, although, unfortunately, I am not now in contact with the original author. A diagram below, has been redrawn on the basis of the clay mineralogy work of Holmes. Minor changes have been made to update the terminology (i.e. montmorillonite to smectite).

Summarised clay mineralogy of the strata at the east side of Lulworth Cove, Dorset, redrawn from the unpublished study by I.F. Holmes, 1975


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Please go to:



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Go to Lulworth Cove Bibliography?

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[section to be expanded when time permits]


The view eastward across Lulworth Cove, Dorset, with questions on inversion tectonics, petroleum geology and other matters, as a student exercise


2. Explain why residual oil is found near the Purbeck-Wealden junction in the Lulworth area (Mupe Bay to Dungy Head) but never in higher strata, such as the Upper Greensand, commenting on the date and mechanism of migration.


3. Why are gas seeps occurring mainly at Lulworth Banks, offshore, and at Durlston Head now? When did they probably occur on a large scale at or near Lulworth Cove?


4. What, if any, is the relationship between the occurrence of the Stair Hole Seismite and the hydrocarbon seepage. What,if any, is the relationship to the Bay of Biscay?


[questions to be added]

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I am very grateful to the many geologists who have accompanied me in Lulworth Cove over the years and discussed aspects of the geology. I am sorry that I cannot name them all. Discussion with students involved in research projects has been very helpful. I thank Louise Morris for useful contributions to the topic of the source of the Lulworth Cove beach pebbles. I very much appreciate the kindness of Professor Adam El-Shahat in allowing me to make use of his excellent work on the Purbeck Group in 1977. I thank Halfdan Carsten for his kind permission to use photographs taken on a field trip in Dorset in 2005. I think Philip Prince for showing me his extremely interesting modelling of the Inversion Structure on Utube. The support and encouragement during the development of these pages by the staff of the National Oceanography Centre, Southampton (formerly Southampton Oceanography Centre) is very much appreciated. The academic staff and students of various field trips at Lulworth Cove are thanked for their kind cooperation regarding photography on the cliffs. I particularly thank Professor Jonathon Bull, Associate Dean of the Faculty of Natural Science and the Environment at Southampton University for supporting the continuation of this website through Southampton University; this is much appreciated.

My late wife Catherine West very kindly provided background support for the production of this and all the other webpages, and I very much appreciated her help. I very much appreciate the advice and help of our daughters, Tonya and Joanna. In particular, Tonya Loades of Bartley West, Chartered Surveyors has provided much help with the website and with associated organisational matters.

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|Home and Contents |Stair Hole, Lulworth |Fossil Forest | Dungy Head and St. Oswald's Bay |Durdle Door |Mupe Bay |Worbarrow Bay

Copyright © 2020 Ian West, Tonya Loades and Joanna Bentley. All rights reserved. This is a private, academic website intended to be useful for research, reference and educational purposes. Images and text may not be copied for publication or for use on other webpages such as MOOCs or for any commercial activity. A reasonable number of images and some text may be used for non-commercial, non-charged, non-online and non- published academic purposes, including field trip handouts, student projects, dissertations etc, providing the source is acknowledged. All images so used must contain the original caption, including the copyright statement. Some images are not those of the author and the copyright is that of the original photographer and these are not for any use without specific permission from the source photographer. This particularly applies to aerial photographs, but also to some sets of field photographs.

Disclaimer: Geological fieldwork involves some level of risk, which can be reduced by knowledge, experience and appropriate safety precautions. Persons undertaking field work should assess the risk, as far as possible, in accordance with weather, conditions on the day and the type of persons involved. In providing field guides on the Internet no person is advised here to undertake geological field work in any way that might involve them in unreasonable risk from cliffs, ledges, rocks, sea or other causes. Not all places need be visited and the descriptions and photographs here can be used as an alternative to visiting. Individuals and leaders should take appropriate safety precautions, and in bad conditions be prepared to cancell part or all of the field trip if necessary. Permission should be sought for entry into private land and no damage should take place. Attention should be paid to weather warnings, local warnings and danger signs. No liability for death, injury, damage to, or loss of property in connection with a field trip is accepted by providing these websites of geological information. Discussion of geological and geomorphological features, coast erosion, coastal retreat, storm surges etc are given here for academic and educational purposes only. They are not intended for assessment of risk to property or to life. No liability is accepted if this website is used beyond its academic purposes in attempting to determine measures of risk to life or property.

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Dr Ian West, author of these webpages

Webpage - written and produced by:

Ian West, M.Sc. Ph.D. F.G.S.


at his private address, Romsey, Hampshire, kindly supported by Southampton University,and web-hosted by courtesy of iSolutions of Southampton University. The website does not necessarily represent the views of Southampton University. The website is written privately from home in Romsey, unfunded and with no staff other than the author, but generously and freely published by Southampton University. Field trips shown in photographs do not necessarily have any connection with Southampton University and may have been private or have been run by various organisations.

Ian West, more than 60 years geology on the Dorset Coast